hard writing question

Test Preparation SAT Preparation
1

hi guys

1, because the number of hawaiian monk seals in the wild[have decreased] dramatically since 1989, conservationists fear that these endangered animals may soon become extinct.
A. have decreased
B. have been decreasing
C. has decreased

i picked B cause the question uses ‘since’ meaning that its coming from the past to the present so i would use a present prefect, however, CB said it is C, any explainations?

2.[ if properly maintained, a bicycle can last for decades, providing ]recreation, transportation, and exercise opportunities for its owner.
A.if properly maintained, a bicycle can last for decades, providing
B properly maintained, a bicycle that lasts for decades, providing
C if a bicycle is properly maintained, then it can last for decades and providing
D when a bicycle is maintained properly, it can last for decades, it can provide
E when you maintain your bicycle properly, it can last for decades and provide one with

I picked D but CB is A, i crossed A because since a bicycle is between 2 commas it would count as a nonessential clause.
and for D would adding ‘When’ to an independent clause make it a depend clause?

cheers

2

For the first one, It would be ‘have’ if you changed the word ‘number’ to ‘numbers.’ But the word is ‘number’ so you would use has.

3
  1. "The number of" is singular; "a number of" is plural.
  2. "Between two commas" doesn't always render a clause nonessential. In this case, the preceding phrase ("If properly maintained") is a modifier, not a clause, so the one including "a bicycle" is its anchor and thus the main clause of the sentence. For (D), adding "when" does NOT make the clause dependent, because it's a modifier phrase rather than a clause! Compare: "When studying for the SAT, one must not cut corners."--the stuff before the comma is the modifier, the stuff after is the clause.