问题 填空题

活塞式抽水机和离心式水泵,都是利用______把水从低处抽到高处的,因此要把抽水机正常工作,它离水面的距离不得超过______m.

答案

活塞式抽水机和离心式抽水机工作时,都是使其内部气压小于外界大气压,在外界大气压的作用下将水压入抽水机内,进而实现把水从低处压到高处的目的.

由公式p=ρgh得,h=

P
ρg
=
1.01×105Pa
1000kg/m3×9.8N/kg
≈10.3m.也就是说大气压只能支持高10.3m的水柱,而离心式抽水机又是利用了大气压的作用,所以它离水面的高度不得超过这一数值.

故答案是:大气压;10.3.

阅读理解

We now think of chocolate as sweet, but once it was bitter. We think of it as a candy, but once it was a medicine. Today, chocolate can be a hot drink, a frozen dessert, or just a snack. Sometimes it’s an ingredient(配料) in the main course of a meal. Mexicans make a hot chocolate sauce called mole and pour it over chicken. The Mexicans also eat chocolate with spices(香料) like chili peppers.

Chocolate is a product of the tropical cacao tree. The beans taste so bitter that even the monkeys say “Ugh!” and run away. Workers must first dry and then roast the beans. This removes the bitter taste.

The word “chocolate” comes from a Mayan word. The Mayas were an ancient people who once lived in Mexico. They valued the cacao tree. Some used the beans for money, while others crushed them to make a drink.

When the Spaniards came to Mexico in the sixteenth century, they started drinking cacao too.Because the drink was strong and bitter, they thought it was a medicine. No one had the idea of adding sugar. The Spaniards took some beans back to Europe and opened cafes. Wealthy people drank cacao and said it was good for the digestion.

In the 1800s, the owner of a chocolate factory in England discovered that sugar removed the bitter taste of cacao. It quickly became a cheap and popular drink. Soon afterwards, a factory made the first solid block of sweetened chocolate. Later on, another factory mixed milk and chocolate together. People liked the taste of milk chocolate even better.

Besides the chocolate candy bar, one of the most popular American snacks is the chocolate chip cookie. Favorite desserts are chocolate cream pie and, of course, an ice cream sundae with hot fudge sauce.  

1. It was ________that discovered sugar could remove the bitter taste of cacao.

A. The workers in the chocolate factory       B. The Spaniards

C. The people in England                 D. The owner of a chocolate factory

2. According to the passage which of the following statements is true?

A. Nobody had the idea of adding sugar until the sixteenth century.

B. The word “chocolate” comes from a Mexican word.

C. The beans taste so bitter that even the monkeys like them.

D. Workers must dry and roast the beans to remove the bitter taste.

3. The Spaniards think that cacao was a medicine because________

A. it was strong and bitter.    B. it was good for digestion.

C. it cured man’s diseases.     D. it was a kind of drink for good health.

4. Which is the right time order of the events regarding chocolate?

a. Chocolate became a cheap and popular drink in England.

b. A factory made the first solid block of sweetened chocolate.

c. The Spaniards started drinking cacao.

d. It was found that sugar removed the bitter taste of cacao.

e. A factory mixed milk and chocolate together.  

A. a-b-c-d-e           B. c-d-e-b-a    C. c-d-a-b-e          D. c-d-b-e-a

5. It can be inferred from the passage that ________.

A. chocolate can be a hot drink, a frozen dessert, or a candy bar

B. Mexicans like chocolate very much

C. chocolate is a product of the cacao tree

D. people liked the taste of chocolate mixed with milk

选择题