问题 填空题

  • A.条件(1)充分,但条件(2)不充分
  • B.条件(2)充分,但条件(1)不充分
  • C.条件(1)和条件(2)单独都不充分,但条件(1)和条件(2)联合起来充分
  • D.条件(1)充分,条件(2)也充分
  • E.条件(1)和条件(2)单独都不充分,条件(1)和(2)联合起来也不充分

某学习小组男女生共有8人,现从男生中选2人,从女生中选1人,分别担任三种不同的工作,共有90种不同的选法.
(1) 该小组有男生3人,女生5人 (2) 该小组有男生5人,女生3人

答案

参考答案:A

解析: 本题应分两步:首先,要选出所用的人,现设男生共有x人,则女生为(8-x)人,由于男生只能从男生中取,故有[*]种.
同理,女生的取法有[*]种,故选人的方法为[*];其次把选出的学生分配出去的方法有[*],故3x(x-1)(8-x)=90,即x(x-1)(8-x)=30=2×3×5,则x=5或x=3,当x=5为增根(舍);当x=3时,满足题意,故有男生3人,女生5人,即条件(1)充分,条件(2)不充分.此题也可以直接从条件(1)和条件(2)所给的值下手.
故正确答案为A.

阅读理解

阅读理解。

     Some people may think too much sunlight can lead to cancer, so they always keep themselves away

from sunlight. But experts believe that proper exposure (暴露) to sunlight is good for us.

     For example, scientists think sunlight can help stop some diseases. They say that wearing sunscreen

(防晒油) all the time makes the body short of vitamin D.

     Vitamin D in fact stops us from more than 25 diseases and keeps bones and teeth healthy. However,

around 60% of the population are short of vitamin D in their blood. One of the easiest ways to get it is to

expose your skin to sunlight. Your body makes vitamin D from the sun faster than it takes in from food.

What's more, safely getting enough sunlight can make you look younger.

     However, not everybody likes sunlight. Some people should not be exposed to the sun without a strong

sun protection. Experts advise that just ten minutes of daily exposure to sunlight should be enough to give

us vitamin D we need.

1. What does the passage mainly tell us?

A. Don't expose to the sun.

B. Proper exposure to sunlight is good for our health.

C. We should stay in the sun as long as possible.

D. We can get vitamin D from food.

2. What will happen if we don't get enough sunlight for a long time? 

A. We will keep away from cancer.

B. We will get many diseases.

C. Our body will be short of vitamin D.

D. We will have more vitamin D in our blood.

3. The proper sunshine can keep our _______ healthy.

A. eyes and skin

B. bones and teeth

C. ears and blood

D. bones and eyes

4. The underlined phrase"take in" in the passage means "_______" in Chinese.

A. 吸收

B. 占用

C. 分享

D. 拿进来

5. Which is NOT true according to the passage? 

A. Scientists think our skin can get vitamin D from sunlight.

B. Most people have enough vitamin D in their blood.

C. Ten minutes of exposure to sunlight every day is enough for us to get vitamin D.

D. Our body gets vitamin D faster from the sun than from food.

单项选择题