豌豆在自然状态下是纯种的原因( )
A:豌豆品种间的性状差异很大
B:豌豆先开花后传粉
C:豌豆是自花传粉闭花传粉的植物
D:豌豆是自花传粉的植物
下列各句中,划线的成语使用恰当的一句是( )
⑴I'm hungry.____ A. She's running.
⑵What are you doing?____ B. He's making noodles.
⑶What are they doing?____ C. I'm hungry, too.
⑷What is she doing?____ D. They are rowing a boat.
⑸What is Sam doing?____ E. I'm reading a book.