If additional deposits of oil are found,
it will expand the amount that can be used as fuel and reduce the price of oil, even if the deposits are not immediately tapped.
(A) it will expand the amount that can be used as fuel and reduce the price of oil
"expand" isnt't right to modify "amount". We should use "increase".
"it" is wrong. This "it" can only refer to "oil". However, the "oil" itself cannot reduce the price of oil (itself). It is the "additional deposits of oil" that reduces the price.
(B) the amount that is able to be used as fuel will expand and the price of oil be reduced
In gmat, "can" is better than "be able to". So we should lookout for a "can" in the later answer choices.
"expand" is wrong, same as A.
"be reduced" seems like the price is reduced by some human forces. However, it is the additional deposits or the force of market. (C) it will cause an increase in the amount that is able to be used as fuel and a reduction in the price of oil
"it" is wrong, same as A.(D) the amount that can be used as fuel will increase and the price of oil will drop
(E) it will increase the amount of oil that can be used as fuel and cause a drop in the price
"it" is wrong, same as A.