下列叙述，不正确的是（ ） A．性染色体只存在于性细胞中 B．成对的基因分别位于

我国公安机关工作的宗旨是全心全意为人民服务。 ( )

根据句意及所给单词的首字母提示填空。

1. The start of the New Year is the b        of a l0-day celebration.

2. Halloween is very popular in the w         countries.

3. He cut his finger with a s          knife.

4. The old man lives here. He is the o         of this house.

5. Rice dumplings are the t         food of Chinese for the Dragon Boat Festival.

用所给词的适当形式填空。

1. We think the charity show is a _________ (meaning) activity and we'll take part in it.

2. Today's newspaper says _________ (clear) that middle students can only be at school for no more than

    seven hours a day.

3. They _________ (work) in the nature reserve over the years.

4. —What an interesting book!    —I have the same _________ (feel). I will read it again when I have time.

5. Edddie's mother was ill after _________ (wait) for him in the rain for a long time.

6. Timmy _________ (trap) under the stones and bricks, so he shouted for help.

7. —Where were you at this time last night?    —I _________ (write) an e-mail at home.

8. The best way to learn English is to practice _________ (speak) it.

某车床车螺纹时螺纹的导程发生了周期性的误差，则调整机床时应注意调整( )

A．导轨在垂直面内的平行度误差
B．主轴轴向窜动误差
C．主轴的角度摆动误差
D．传动链的误差

合成PET的主要原料有（）

A、对苯二甲酸（PTA.

B、对苯二甲酸二甲脂（DMT）

C、乙二醇（MEG）

D、丙三醇