A：watch
B：to watch
C：watching
D：watched
Bob likes pictures. He can very much.
对卵细胞、胚泡、受精卵、胎儿、胚胎几个生理名词，按照形成的先后排序正确的是（ ）
You ______a teacher. I ______ a student. My sister ______a student, too.
