超声波是频率为20000Hz以上的高频弹性波，次声波是频率低于20Hz_爱下问搜题

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问题选择题

超声波是频率为20000Hz以上的高频弹性波，次声波是频率低于20Hz的低频弹性波．已知人体内脏器官的振荡频率为4-18Hz．在强度较大且强度相同的情况下，对人体伤害最大的是（　　）

A．可闻声波

B．超声波

C．次声波

D．它们对人体的伤害是相同的

答案

答案：C

填空题

阅读下面短文，从所给单词中选出适当的词，并用其正确的语言形式填在标有题号的空白处，使语意通顺、完整。（每空一词且每个单词只能用一次）

orange vegetable plant prepare eat taste field during and cool bright enough as usual fact

Carrots(胡萝卜) are grown on farms and in small family gardens all over the world. They are easy to _小题1:___ and easy to harvest(收获). They have a good __小题2:_.
When people think about carrots, they 小题3:think they are a kind of long, thin, orange-colored vegetable. In _小题4:_, carrots are in many different sizes and shapes. And not all carrots are __小题5:_.
Carrots should be grown in a _小题6:_ that does not have water for a long time. The earth also should not be too hard. To ___小题7:__ your carrot garden, dig up the earth and turn it over(翻土).
Weather, soil condition(土壤状况), __小题8:__ time affect(影响) the taste of carrots. Warm days and __小题9:_ nights are the best time to grow great delicious carrots.
The best way to decide if a carrot is ready to be harvested is by its color. Usually, the __小题10:__the color is, the better the taste is.
Most people do not know that carrots can be grown __小题11:__ the winter months. If the winter is not cold __小题12:_ to freeze the ground, you can grow carrots the same way __小题13: you do during the summer months.
Carrots are prepared and __小题14:_ in many different ways. They are cut into thin pieces and cooked with other _小题15:_ or meat. Or, they are washed, and eaten just as they come out of the ground.

问答题简答题

试述隋唐科举制度。