性病的控制对预防HIV的流行非常有价值，这是因为（）。 A.患者有病会及时到医院去就

句型转换。

1. They have never been to an English-speaking country. (变为一般疑问句)

                 they             been to an English-speaking country?

2. She has been a flight attendant for two years. (对画线部分提问)

                               has she been a flight attendant?

3. His father has been to America twice. (对画线部分提问)

                has his father been to America?

4. Linda is taller than any other girl in her class.(改为同义句)

    Linda is                         girl in her class.

5. I prefer tea to coffee.(改为同义句)

    I prefer to have tea              have coffee.

如果关系模式R的属性之间不存在非平凡且非函数依赖的多值依赖，则R的规范化程序达到了______。

哪项参数用来控制异步电动机的速率？（）

A.电压

B.频率

C.电流

D.相位角

我国历年城乡居民储蓄构成（%）

1978年与1957年相比，城镇居民储蓄所占比重下降了多少（）

A．6.3

B．6.3％

C．5.8

D．5.8％

下列哪一种植物与其它三种不属于同一生活型（）

A、仙人掌

B、景天

C、芦荟

D、吊兰