题目

Generally speaking，          according to the directions，the drug has no side effect．    A．when to take       B．when taken       C．when taking    D．when to be taken 答案：B16．如图，在正方形ABCD中，E是BC的中点，F是CD上一点，且CF=$\frac{1}{4}$CD，下列结论：①∠BAE=30°，②△ABE～△AEF，③AE⊥EF，④△ADF～△ECF．其中正确的有②③．