Sentence Correction (SC) | Re: By 1940, the pilot Jacqueline Cochran held seventeen

A. and she earned them at a time when aviation was still so new for many of the planes she flew tobe------ flew to be -- is bad usage; to be is not a verb. We need a past tense verb such as were to mark the plural subject planes. (For is used in the menaing of because)

B. earning them at a time that aviation was still so new for many of the planes she flew were--- at a time needs when as the relative pronoun

C