(A) Know become knew
Reason : it is past tense.
2) The languages of the world (presents) a vast (array) of structural (similarities) and (differences).
(A) Presents become present
Reason : "languages" is plural, and plural doesn't use "s" in its sentences.
3) The rise of multinationals (have) (resulted) in a great deal of legal ambiguity because multinationals (can) (operate)) in so many jurisdictions.
(A) Have become has
Reason : the rise of multinationals is singular, and singular doesn't use "have" but it uses "has".
4) All of the east-west interstate highways in the United States (has) even (numbers), while north-south interstate highways (are) (odd-numbered).
(A) Has become have
Reason : the subject is plural and it has to use "have" instead of "has"
5) (When) a massive star in the large Magellanic Cloud (exploded) in 1987, a wave of neutrinous (were) (detected) on earth.
(C) Were become was
Reason : the subject is singular so "were" is not correct for it.
6) Every open space in the (targeted) area that (has) grass and a few bushes (are) (occupied) by the white-crowned sparrow.
(C) Are become isReason : every + (noun) is grammatically singular, so it uses "is" for the verb.
7) Krakatoa (is remembered) as the volcano that (put) so much ash into the air that sunsets around the world (was affected) for two years (afterward).
(A) Is remembered become was rememberedReason : the sentence is a pas tense, so it uses "was" instead of "is"
8) The term "Yankee" (was) originally a nickname for people from New England, but now anyone from the United States (are) (referred) (to as) a Yankee.
(B) Are become isReason : anyone is grammatically singular, so we use is for the verb
9) A network of small arteries, mostly (sandwiched) between the skin and the (underlying) muscles, (supply) (blood) to the face and scalp.
(C) Supply become supplies.
Reason : "supply" is subtituted by supplies because of the subject is singular.
10) Mesquite (is) a (small) tree in the Southwest (who) can (withstand) the severest drought.
(C) Who become which.
Reason : I don't know, putting "who" in that sentence is just doesn't make any sense for me.
