物质发生化学变化的本质特征是： A．状态发生变化 B．有气_爱下问搜题

搜题请搜索小程序“爱下问搜题”

问题选择题

物质发生化学变化的本质特征是：

A．状态发生变化

B．有气体放出

C．颜色发生改变

D．有新物质生成

答案

答案：D

从概念上分析，化学变化的本质是新物质的形成过程，所以本质特征就是新物质的生成．而伴随的现象可以用来辅助说明变化的发生，但是现象发生变化并不是最判断化学变化的根据．此题可用排除法解，根据化学变化的概念着手，化学变化的实质是有其他物质生成，故答案D是正确的，而A、B、C、都是化学变化经常伴随的现象，并不是化学变化必须具备的条件，因此A、B、C错误．

故选D．D、化学变化的本质是新物质的形成过程，所以本质特征就是新物质的生成．

完形填空

           Last Sunday we had a fantastic trip. My father, my mother and  I   1 to summer camp.
We went to the mountains. First we   2   to the foot (脚)of the mountain   3   bus. In the middle
of the mountain there was a river(河). The water was clean. I washed my face (洗脸)   4 the
water. It was warm. There   5 some fishes in the river. In the mountain there Were flowers (花).
They were very   6   . At  12 o'clock,many people got together(在一起),and they were very   7
we made our lunch in the mountain. The food was very   8 , and we liked it very much. After
lunch,we went on our trip. Last,we got to the top(顶)of the mountain. We were very   9   It was
really   10 .

( )1. A. go
( )2. A. get
( )3. A. by
( )4. A. on
( )5. A. is
( )6. A. ugly
( )7. A. mart
( )8. A. awful
( )9. A. happy
( )10.A. terrible

B. goes
B. got
B. on
B. with
B. were
B. hungry
B. sad
B. delicious
B. unhappy
B. cold

C. went
C. gets
C. in
C. in
C. was
C. beautiful
C. busy
C. expensive
C. interesting
C. fun

D. going
D. getting
D. at
D. at
D. are
D. awful
D. clever
D. cheap
D. sad
D. hot

单项选择题

切断工件时，工件端面凸起或者凹下，原因可能是（）。

A、丝杆间隙过大

B、切削进给速度过大

C、刀具已经磨损

D、两副偏角过大且不对称