The spraying of pesticides can be carefully planned, but accidents, weather conditions that could not be foreseen, and pilot errors often cause much larger deposits of spray than they had anticipated. (A) weather conditions that could not be foreseen, and pilot errors often cause much larger deposits of spray than they had (B) weather conditions that cannot be foreseen, and pilot errors often cause much larger deposits of spray than (C) unforeseeable weather conditions, and pilot errors are the cause of much larger deposits of spray than they had (D) weather conditions that are not foreseeable, and pilot errors often cause much larger deposits of spray than (E) unforeseeable weather conditions, and pilot errors often cause much larger deposits of spray than they had

B) weather conditions that cannot be foreseen, and pilot errors often cause much larger deposits of spray than

Explanation:

Option B obeys the principle of parallelism because the two phrases, " can be carefully planned" and "cannot be foreseen" follow the same grammatical structure. Option A does not obey parallelism because " can be carefully planned" and "could not be foreseen" do not follow the same grammatical structure.

The phrase " they had anticipated" in the other options apart from B do not have a matching subject. Pilot errors is the subject in this sentence and it is not expected to anticipate anything, only the pilots can.

Moreover, "that cannot be foreseen" is more parallel to "can be carefully planned" that "unforeseeable" or "foreseeable" used in the other options