神经系统结构和功能的基本单位是神经元．

蝴蝶是由“毛毛虫”发育来的，“毛毛虫”在蝴蝶的一生中所处的时期是（   ）

——Do you think Peter is free today?

——__________. He is really busy preparing(准备) for the coming test these days.

________furs in all his life, the old man's biggest wish was to buy a diamond necklace for his beloved wife.