A:①②
B:②③
C:②④
D:①④
史前社会人类面临的环境问题有( )
①洪水 ②猛兽 ③风暴 ④废气
① What are you doing? ____ A. No,she isn't.
② What is your mum doing? ____ B. Yes I am.
③ Can I use your pen? ____ C. I'm cleaning my room.
④ Is Sarah reading a book? ____ D. She is cooking fish.
⑤ Are yoy doing homework? ____ E. Sure.
学习是____ 不断地接受刺激、获得新的____ 、习惯和积累经验的过程.
下面对黄土高原的描述不对的是 ( )