问题 问答题 简答题

什么是机械振动和机械波?二者有何关系?

答案

参考答案:

物体沿着直线或曲线在某一平衡位置附近作往复周期性的运动,成为机械运动。机械振动在弹性介质中传播就产生机械波,振动是产生波动的根源,而波动是振动是振动这一运动方式在介质中的扩展。

阅读理解

The food guide pyramid(金字塔)was the model for healthy eating in the United States. Now it has been replaced(代替)by a colorful plate—called MyPlate—with some of the same messages: Eat different kinds of foods, and eat less of some foods and more of others.

The pyramid has six parts to show the five food groups and fats, oils and sweets. Basic(基本的)foods are at the bottom(底部)and include bread and rice. In two middle parts are vegetables and fruits. In two top parts are milk and cheese, and meat, fish, eggs and so on.

The plate has four parts: vegetables, fruits, grains, and protein, and a side order of dairy(乳制品)in blue. The big message is that fruits and vegetables take up half the plate and the vegetable part is a little bigger than the fruit part. The grain part is bigger than the protein part. The MyPlate seems to be encouraging us to eat different food groups at each meal.

First Lady, Michelle Obama, has introduced the plate. And she will use it with her family. She said the pyramid just wasn’t easy enough for parents and kids to follow.

小题1: MyPlate is for_______.

A.weight training

B.healthy eating

C.protecting animals

D.sleeping well小题2:Which are in the highest part of the pyramid?

A.Meat, fish and eggs.

B.Vegetables and fruits.

C.Bread and rice.

D.Fats, oils and sweets.小题3:According to the passage, which is TRUE?

a. vegetables b. fruits c. grains d. protein e. dairy

A.

B.

C.

D.小题4:The following words can describe the plate EXCEPT_______.

A.colorful

B.wasteful

C.simple

D.useful小题5:We can infer from the last paragraph that_______.

A.First Lady, Michelle Obama, likes the plate

B.Michelle Obama invented the plate

C.First Lady’s family don’t want to use the plate

D.the pyramid is too difficult for us to follow

单项选择题