Obscure Dash Usage on the PSAT

There are two rules that a student needs to know about the long dash (or em dash):\.

(1) One long dash is equivalent to a colon;
(2) Two long dashes are equivalent to commas around a nonessential (or nonrestrictive).

I have never seen a long dash in an ACT English question that didn't fall under one of these rules two rules. The College Board, however, likes to mess with student's (and tutor's) heads by finding obscure dash usages.

For example, question 15, from the 10-15-16 PSAT:

Stress levels, immune system strength, male fertility, and weight and cholesterol— 15 which all appear to benefit from the regular consumption of nuts.

A)  NO CHANGE 
B)  that all appear
C)  all appearing
D)  all appear

Answer choice D would work perfectly if not for that dash: "Stress levels, immune system strength, male fertility, and weight and cholesterol all appear to benefit from the regular consumption of nuts." Unfortunately, the dash is not underlined so there is no way to get rid of it. 

Applying Rule #1, the dash is equivalent to a colon, but the colon is supposed to be preceded by an independent clause. One of the most common uses of a colon INDEPENDENT CLAUSE-COLON-LIST, but here it's LIST-COLON-INDEPENDENT CLAUSE.

Is that even legit?

Apparently it is, according to several grammar websites I found, although none of them explained how this fit in with the rule that a colon must be preceded by an independent clause.

Another obscure dash rule came up in question #3 from from the 11-2-17 PSAT:

A turning point in the musical  3 genre; however, came with Richard Rogers and Oscar Hammerstein II's 4 Oklahoma!

A) NO CHANGE

B) genre, however;

C) genre—however—

D) genre, however,

My first instinct here is to eliminate both C and D because two dashes are equivalent to two commas around the nonessential "however." However, a semicolon may only be used between two independent clauses, and "a turning point in the musical genre" sure ain't an independent clause—with or without the "however." So I'm left choosing between two forms of equivalent punctuation.

The key to the answer lies in the following question:

The writer is considering revising the underlined portion to the following.

Oklahoma!—the first musical to feature a sophisticated story served by music and dance elements.

Should the writer make this revision?

It turns out that the author should make that revision, which leaves the following sentence: "A turning point in the musical genre, however, came with Richard Rogers and Oscar Hammerstein II's Oklahoma!—the first musical to feature a sophisticated story served by music and dance elements." 

Now there is a reason to prefer D over C. While the two dashes in C are equivalent to the two commas in D, using three dashes in one sentence is frowned upon because it may create ambiguity. So the fact that the answer to #4 adds another dash to the sentence determines the correct answer to #3.

 

However v. Nevertheless

However and nevertheless are often synonymous, but not always. “However” can always be used in place of “nevertheless,” but “nevertheless” cannot always replace “however.”




Both words draw a contrast, but “however” merely points out the contrast; “nevertheless,” conveys the added idea that the contrast is surprising. “Nevertheless” means “despite that.”


1a) The full-sized van carries more passengers than the mini-van. 
1b) However, the mini-van gets better gas mileage. 

2a) The full-sized van carries more passengers than the mini-van. 
2b) Nevertheless, the full-sized van gets better mileage.

Both pairs of sentences draw contrasts between the full-sized van and the minivan, but the first contrast is expected. There is nothing surprising about the smaller vehicle getting better mileage than a bigger one. Only "however" is proper here. “Nevertheless” would not make sense.

In the the second pair of sentences, the contrast is surprising. Despite the fact that the full-sized van is bigger than the minivan--i.e., it holds more people--it also gets better mileage.  Either “however” or “nevertheless” would be proper here.


I don’t recall the ACT ever requiring the student to choose between “however” and “nevertheless,” but the SAT did so on Practice Test 2.

It has long been known that the sea otters living along the West Coast of North America help keep kelp forests in their habitat healthy and vital. They do this by feeding on sea urchins and other herbivorous invertebrates that graze voraciously on kelp. With sea otters to keep the population of sea urchins in check, kelp forests can flourish. In fact, even two years or less of sea otter presence can reduce the sea urchin threat in a coastal area Without sea otters present, nevertheless, kelp forests run the danger of becoming barren stretches of coastal wasteland known as urchin barrens.

25                                                                                                                                                

A) NO CHANGE
B) however,
C) hence,
D) likewise,

Here there is nothing surprising about what happens when there are no sea otters, so "nevertheless" is inappropriate.

Of course, the College Board's explanation is not particularly helpful:

Choice B is the best answer because the conjunctive adverb "however” accurately communicates the contrast between an environment shaped by the presence of sea otters, described in the preceding sentence, and an environment shaped by the absence of sea otters, described in this sentence.
Choices A, C, and D are incorrect because each presents a conjunctive adverb that does not accurately depict the relationship between the preceding sentence and the sentence with the underlined word.

In other words, "nevertheless" is wrong because it's not right.