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问题 选择题

按规律排列的一串数2，5，9，14，…这串数的第19个数是（　　）

A．207

B．209

C．211

D．213

答案

2+3+4+5+…+19+20，

=（1+20）×（20÷2）-1，

=21×10-1，

=209；

答：第19个数是209．

故选：B．

填空题

选择正确的词填空。

1. There are a lots of things ____ I need to buy before  the trip.(that, who)

2. Summer is the time of year ____ the day is longer.  (that, which, when)

3. The computer ____ last week works well.(which we bought it, that we bought it, we bought, what

we bought)

4.A good friend is someone ____ makes me happy.  (which, /, that)

5. The young lady ____ you talked with is Lynn's mother.(whom, whose)
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单项选择题

下列道具材料中过硬性最好的是（）

A.碳素工具钢

B.普通高速钢

C.硬质合金

D.含钴高速钢
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