I will go with option B)

grandh01 wrote:Car owners who inflate their tires properly can substantially boost their vehicles fuel
efficiency since the increase in car-road friction can waste up to five percent of car fuel
by under inflation.
(A) Car owners who inflate their tires properly can substantially boost their vehicles' fuel efficiency, since the increase in car-road friction can waste up to five percent
of car fuel by under inflation
(B) Because the under inflation of tires can waste up to five percent of a car's fuel by increasing car-road friction car owners can substantially boost their vehicles' fuel efficiency by properly inflating the tires
(C) Their vehicles' fuel efficiency is substantially boosted by car owners through the proper inflation of tires that, when under inflated can waste up to five percent of
car fuel by an increase in car-road friction
(D) The proper inflation of tires by car owners, due to the fact that under inflation can waste up to five percent of a car's fuel by the increase of car-road friction, can
substantially boost their fuel efficiency
(E) Because up to five percent of a car's fuel are wasted through the increases in car-road friction when the tires are under inflated car owners properly inflating tires can substantially boost their fuel efficiency

OA IS B

option B is the best

Car owners who inflate their tires properly can substantially boost their vehicles fuel
efficiency since the increase in car-road friction can waste up to five percent of car fuel
by under inflation.
(A) Car owners who inflate their tires properly can substantially boost their vehicles'
fuel efficiency, since the increase in car-road friction can waste up to five percent
of car fuel by under inflation
(B) Because the under inflation of tires can waste up to five percent of a car's fuel by
increasing car-road friction car owners can substantially boost their vehicles' fuel
efficiency by properly inflating the tires
(C) Their vehicles' fuel efficiency is substantially boosted by car owners through the
proper inflation of tires that, when under inflated can waste up to five percent of
car fuel by an increase in car-road friction
(D) The proper inflation of tires by car owners, due to the fact that under inflation can
waste up to five percent of a car's fuel by the increase of car-road friction, can
substantially boost their fuel efficiency
(E) Because up to five percent of a car's fuel are wasted through the increases in
car-road friction when the tires are under inflated car owners properly inflating
tires can substantially boost their fuel efficiency
- Option A - Issue A is with pronoun "their". It is referring back to "Cars" that is acting as an adjective here. I think the issue also lies with the second part of the sentence - "since the increase in car-road friction can waste up to five percent of car fuel by under inflation ". I think it should be due to under inflation

- Option B - Nothing seems to be issue except for passive voice. If there had been an better option in Active voice. This could have been eliminated

- Option C - "Their" again is ambiguous. It can't refer to "Cars" as it is acting as an adjective

- Option D - "due to the fact that under inflation can waste up to five percent of a car's fuel by the increase of car-road friction" - what is it modifying

- "are" is incorrect as noun phrases are singular. "Increases" is incorrect. It should be "increase". "Their" has no proper antecedent