填空题。

1. A _____ sea has no, or only small waves, and a _____ film has no speech.

2. There is an article that _____ the rise of the prices. (concern)

3. The children are rather _____ about their mother's health. (concern)

4. Officials should _____ themselves _____ public affairs. (concern)

5. During his last lecture, the scientist _____ (觉得) easier to explain the theory

    to those with some background knowledge. (find)

6. We're going to play basketball. Would you like to _____? (join in / attend)

家养禽畜和栽培作物在自然状态下显示出丰富的多样性，这主要是长期受人工选择的影响。下列关于人工选择的叙述，不正确的是 [ ]

A．人们对生物的性状选择有多方面的需要

B．人工方法能获得更多的变异来源

C．人们通过生产活动能创造更丰富的环境条件，使对人类有利的变异得到保存

D．人工选择可不受自然条件的制约