改写句子。

1. There are some CDs and hair clips on the desk. (一般疑问句)

     __________ there __________ CDs and hair clips on the desk?

2. He watches CCTV news every day. (改为否定句)

    He _________ __________ CCTV news every day.

3. There are two policemen at the gate. (对划线部分提问)

    __________ __________ policemen are there at the gate?

4. The girl goes to school by bus every day. (同义句) 

    The girl __________ a __________ to school every day.

5. Is he good at Maths? (同义句)

    __________ he __________ well in Maths?

移民流行病学是对移民人群的疾病分布进行研究，以探讨病因。若移民中某病的发病率及死亡率与原居住地人群的发病率或死亡率接近，而与移民地当地居民人群的发病率及死亡率不同，则引起发病率及死亡率差别的主要原因（）

A.遗传因素

B.环境因素

C.遗传和环境交互作用

D.很难判断

E.遗传与环境的独立作用