问题 选择题

关于声音,下列说法中正确的是(   )

A.物体的振幅越大,发出声音的频率越大

B.声音在真空中传播的速度是3×l08m/s

C.街头安装的噪声监测仪可以减弱噪声

D.超声波、次声波是人耳听不到的声音

答案

题目分析:A.振幅会影响发出声音的响度,频率会影响发出声音的音调

B.声音的传播需要介质,一切固、液、气都可传声,真空不能传声

C.噪声监测仪只能显示出噪声的等级并不能减弱噪声

D.人耳的听觉频率范围是20-20000Hz,超声波的频率高于人耳听觉频率上限,次声波的频率低于人耳的听觉频率下限。选项D正确。

填空题
单项选择题

I was a single parent of four small children, working at a low paid job. Money was always tight, but we had a (1) over our heads, food on the table, clothes on our backs, and if not a lot, always (2) . Not knowing we were poor, my kids just thought I was (3) . I’ve always been glad about that.

It was Christmas time, and although there wasn’t (4) for a lot of gifts, we planned to celebrate with a family party. But the big (5) for the kids was the fun of Christmas (6) .

They planned weeks ahead of time, asking (7) what they wanted for Christmas. Fortunately, I had saved MYM120 for (8) to share by all five of us.

The big (9) arrived. I gave each kid a twenty-dollar bill and (10) them to look for gifts of about four dollars each. Then everyone scattered. We had two hours to shop; then we would (11) back at the "Santa’s Workshop".

Driving home, everyone was in high Christmas spirits, (12) my younger daughter, Ginger, who was unusually (13) . She had only one small, flat bag with a few candies—fiftycent candies! I was so angry, but I didn’t say anything (14) we got home. I called her into my bedroom and closed the door, (15) to be angry again. This is what she told me.

"I was looking (16) thinking of what to buy, and I (17) to read the little cards on the ’Giving Trees’. One was for a little girl, four years old, and all she (18) for Christmas was a doll. So I took the card off the tree and (19) the doll for her. We have so much and she doesn’t have anything. "

I never felt so (20) as I did that day.

8()

A.toys 

B.clothes 

C.presents 

D.bills