I thought _______ very useful to know the customs of foreign countries.
A：that
B： to coming
C：it
D：to go
— Alice, could you help me ________ meat? I want to make some dumplings for dinner.
— OK. I'll do it right away.
草履虫把体内多余的水分和部分代谢废物排到体外的结构是( )
