若|a|=1，|b|=2，若(a-b)⊥a，则向量a与b的夹角为______．

已知△ABC与△A′B′C′中，AB=6，BC=8，A′C′=4.5，B′C′=4，要使△ABC∽△A′B′C′，则必有A′B′=______．

根据句意和首字母提示填空。    

1. His telephone n_____ is 7396250.    

2. What kind of d_____ would you like, strawberry ice cream or apple ice cream?    

3. There's o_____ one yuan with me, I can't buy these oranges.

4. We'll have a long vacation! Really? It's g_____!

5. We have many kinds of f_____ and drinks.

What they never take into account is the frazzled woman who is leading a________life — trying to be a good mother while having to pretend at work that she doesn't have kids at all.

A．double

B．hard

C．two-way

D．miserable

单位下发了社保卡，我想了解一下北京社保卡怎么用？怎么激活？