题型:选择题 Sally took a photo of her friends while they ______ computer games.A.playedB.were playingC.had playedD.play 查看答案
题型:单项选择题 关于滋养层发育过程正确的是()A.滋养层外层是细胞滋养细胞B.细胞滋养细胞由合体滋养细胞分化而来C.合体滋养细胞是分裂生长的细胞D.细胞滋养细胞是执行功能的细胞E.滋养层内面有一层细胞称胚外中胚层 查看答案