根据句意及首字母提示完成单词。

1.  —How much is this box?

      —It's seven d__________.

2. —What c__________ is your shirt?

     —It's white, but your shirt is black.

3.  This ruler is too short. I need a l__________ one.

4.  —Do you s__________ watches?

     —Yes, we have lots of new watches.

5.  —What's the p__________ of the coat?

      —It's 50 dollars.

6.  The green shorts are on s__________ for $ 25.

7.  There are t__________ months in a year.

8.  Trousers are called (被叫做) p__________ in American English.

下列哪个指标不用于流行病学实验研究

A．有效率

B．治愈率

C．抗体阳性率

D．保护率

E．引入率