As the price of gasoline rises, which makes substituting alcohol distilled from cereal grain attractive, the prices of bread and livestock feed are sure to increase.
(A) which makes substituting alcohol distilled from cereal grain attractive
(B) which makes substituting the distillation of alcohol from cereal grain attractive
(C) which makes distilling alcohol from cereal grain an attractive substitute
(D) making an attractive substitution of alcohol distilled from cereal grain（E）
(E) making alcohol distilled from cereal grain an attractive substitute
Choice A, B, and C are faulty because the pronoun which refers loosely to the whole clause rather than to some noun.
The original sentence is intended to say that alcohol is an attractive substitute for gasoline, but the understood phrase for gasoline cannot be inserted anywhere in A without producing an awkward construction.
Both B and C are illogically worded: the distillation of alcohol, not the alcohol itself, is substituted for gasoline in B, as the act of distilling alcohol is in C.
Choice D is unidiomatic and suggests that the rising rice of gasoline is what makes the substitution.
Choice E is the best for this question of middle difficulty.