假定所有变量均已正确说明，以下程序段运行后，x的值是______。a=b=c=0；x

氧化铝的输送任务是什么？

跨度为6M、混凝土强度为C30的现浇混凝土板，当混凝土强度至少应达到（）方可拆除底模。

A、15N/mm²

B、21N/mm2

C、22.5N/mm²

D、30N/mm²

下列做法会引起水体污染的是（　　）

①使用含磷洗衣粉；②任意占用耕地；③工业污水任意排放；④大量使用农药；⑤鱼类养殖；⑥生活污水任意排放；⑦乱砍滥伐森林；⑧猎杀野生动物．

A．①②③④⑥

B．③④⑥⑦

C．①③④⑥

D．全部

凸轮机构是一种高副机构，一般由凸轮、（）和机架三构件所组成。

A、主动件

B、从动件

C、运动件

D、转动件

根据所给要求，改写下列句子。每空格限填一词。

1. The new flat cost Mr. Black a lot of money. (改为否定句)

    The new flat ______ cost Mr. Black ______ money.

2. The red bike belongs to my mother. (对划线部分提问)

    ______ ______ belongs to your mother?

3. Whiz-kid Wendy's never late for work.（改为反意疑问句）

   Whiz-kid Wendy's never late for work, _____ _____?

4. The boy is so strong that he can carry the heavy safe easily. (改为简单句)

    The boy is strong ______ ______ carry the heavy safe easily.

5. By the time he was six, he had started learning Japanese. (保持句子原意)

    He ______ learning Japanese ______ he was six.

6. James Nai. Smith, a Canadian doctor invented basketball. (改为被动语态)

    Basketball ______ ______ by James Nai. Smith, a Canadian doctor.