搜题请搜索小程序“爱下问搜题”
问题 选择题
设P为椭圆
x2
16
+
y2
9
=1上的一点，F1、F2是椭圆的焦点，若|PF1|：|PF2|=3：1，则∠F1PF2的大小为（　　）
A．30°B．60°C．90°D．120°
答案

由题意可得 a=4，b=3，|F1F2|=2c=2

7

由于P为椭圆

x2
16
+
y2
9
=1上的一点，

则|PF1|+|PF2|=2a，即2|PF2|=8，

又由|PF1|：|PF2|=3：1，

则|PF2|=2，|PF1|=6，

在三角形F1PF2中，由余弦定理可知，

cos∠F1PF2=

22+62-(2
7
)2
2×2×6
=
1
2

则∠F1PF2的大小为60°，

故选：B．

听力题

Fill in the blanks with the CORRECT form of the word.

小题1: Benjamin Franklin discovered that l_________ is actually electrcity by his kite experiment.

小题2:Kunming is the capital of Yunnan Proveince in s_________ China.

小题3:We decided to make a v_________ down the Yellow River to the sea.

小题4:It is because his v_________ is not big enough that he can’t express himself well in English.

小题5:www.expo2010.cn is the o_________ website of the 2010 Expo in Shanghai China.

小题6:Now the weather is becoming colder _________. (逐渐的)

小题7: He practises speaking English every day so he speaks _________ (流利的) English.

小题8: When you are facing an earthquake, the first thing you have to do is to stay _________. (镇定的)

小题9: It rains _________ (经常性的) these days, which makes him very upset.

小题10: From his strong _________ (口音) we can easily tell he is from London.
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单项选择题

雌激素的周期性变化正确的是：

A．卵泡开始发育时雌激素处于中等水平

B．随着卵泡的发育雌激素分泌逐渐增多

C．于排卵前分泌量逐渐减少

D．排卵后分泌量继续减少

E．黄体萎缩时，分泌量急剧上升
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