... the modifier and the sentence is more fluid without that In B and C, it and that it are intrusive and ungrammatical: the idiom is "believe x to be y." In the context of this sentence, the infinitive ... creates a run-on sentence with no logical connection established between the halves In B, the agreement to the fact is unidiomatic, and B, C, and E alter the sense of the original sentence by saying ... The sentence compares one thing, an adverse change in climate, to all other things in its class that is, to all the possible disasters that threaten American agriculture, therefore, the sentence...