孟德尔的两对相对性状的遗传实验中，具有1：1：1：1比例的是（ ）
①F1产生配子的类型比例 ②F2表现型比例 ③F1测交后代类型比例 ④F1表现型比例 ⑤F2基因型比例．
A：②④
B：①③
C：④⑤
D：②⑤
世界上人口自然增长率最高的大洲是( )
— Let's go hiking ________ staying at home, shall we?
— Good idea.
Clerk: ____ I help you?
Mary: Yes, please. I want a sweater.
Clerk: What ____ do you want?
Mary: Blue.
Clerk: Here you are.
Mary: How ____ is it?
Clerk: Nine dollars.
Mary: I'll ____ it. Thanks.
Clerk: You're ____.
30－20＝____ 80－30＝____ 90－40＝____
10＋50＝____ 30＋60＝____ 70－70＝____
