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问题 选择题
已知一个不透明的袋子里装有6个白球、若干个黑球，如果从中摸出一球是白球的概率是
3
8
，再放入袋子里两个黑球，则摸出一球是黑球的概率是（　　）
A．
2
3
B．
2
9
C．
7
9
D．
1
3
答案

设黑球的个数是x，

∵从中摸出一球是白球的概率是

3
8
，

∴

6
6+x
=
3
8
，解得x=10，

∴若再放入两个黑球，则球的总数为6+10+2=18个，黑球的个数为：10+2=12个，

∴再放入袋子里两个黑球，则摸出一球是黑球的概率是

12
18
=
2
3
．

故选A．

填空题

暑期夏令营里来自中、英两国的小朋友面对下列题目各自有不同的麻烦，你来帮助他们写出合适的单词吧!

1. They are __________(搜查) the forest for the missing boy.

2. Daniel is the most ____________(勤勉的) boy.

3. Mr Green closed the door _________ and left, so nobody noticed him.

4. It is so dark at night that we cannot see ___________(任何人).

5. You can borrow books from the school library ,but you should _________them on time.

6. The bats(蝙蝠) always sleep in the __________and go out for food at night.

7. His grandfather _________(死) five years ago.

8. Would you like to __________ on the moon some day?

9. Look! A snake is moving towards us . It is very__________ .

10. When you leave , you should _________ to turn off the lights.
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单项选择题

患者停经37周，化验检查，HBsAg、HBeAg及HBcAb均阳性。产前咨询。关于乙型病毒性肝炎母婴传播，不正确的是（）

A.HBV可以通过胎盘引起胎儿宫内感染

B.产时传播是乙型肝炎母婴传播的主要途径

C.选择性剖宫产可以避免产时传播

D.产后母乳喂养可造成婴儿HBV感染

E.新生儿可通过接触母亲唾液感染HBV
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