A) the speed with which the Silver Queen corn must be rushed to market soon after picking in order to preserve its sweetness,
Explanation: Illogical comparison between ‘the speed with which…’ and ‘Newly bred varieties’. Also, Unlike must always be followed by noun.
B) Silver Queen corn, having to be rushed to market soon after it is picked to preserve its sweetness,
Explanation: The past tense of the sentence makes the sentence illogical. It is fact and must be presented in present tense. "Having" modifies an entire independent clause but whats before it is not an independent clause. It is a dependent clause “Unlike Silver Queen Corn”. “Having to be rushed soon after it is picked” - must modify a clause- (Giving details about the action/result)
C) Silver Queen corn, which must be rushed to market soon after picking in order to preserve its sweetness, (Correct Answer)
Explanation: ‘Which’ correctly refers to Silver Queen Corn. Which should refer to the noun preceding it before the ‘, + Which’ structure
D) Silver Queen corn, which, by rushing to market soon after picking, can preserve its sweetness,
Explanation: ‘Which’ correctly refers to Silver Queen Corn; however, the usage of commas in the sentence can make some parts of the sentence as a non-essential modifier. Therefore, the sentence is awkward and inconsistent,
E) the sweetness of Silver Queen, which can be preserved only by rushing it to market soon after picking,
Explanation: Illogical comparison between ‘the sweetness of Silver Queen…’ and ‘Newly bred varieties’. Also, Corn is not used here which makes the sentence illogical, since the subject is ‘Silver Queen Corn’ and not the ‘Silver Queen’.