TOEFL Reading: ETS-TOEFL阅读机经 - 534TCW835STPSTU6L$

According to paragraph 3, why is spinach considered a short night plant? A. It will not flower if it experiences too many hours of uninterrupted darkness. B. It flowers after certain number of short nights. C. It flowers as soon as the nights become shorter than the days. D. It flowers for only a short period of time usually at night.