D．her lover

28．The purpose of the passage is to tell us ________.

A．a love story happening between Valentine and a daughter of a guard

B．the history of Valentine's Day and it wins popularity among Chinese young people

C．a priest who loved bravely facing pressure from the emperor

D．that February is a month of romance

　　　　　　　　　　　　　　C

Chemical Change and Physical Change

There are two kinds of changes - chemical change and physical change.

In a chemical change, there is always a new substance formed. Breaking up water into hydrogen and oxygen is a chemical change. In each of the chemical change at least one new substance is formed. A change is not a chemical change if it doesn't form a new substance.

Physical changes are very common, too. There are many examples. You can make a physical change by tearing a piece of paper into two, or by cutting a piece of iron with lathe (机床). Here paper is still paper, and the iron is still iron.

Another way of making physical change is dissolving something in water. When you dissolve salt in water, the salt disappears. You may think that a new substance has been formed. But really there is no new substance. The salt is still salt. You can still taste it. So the dissolving of anything is a physical change.

When water freezes, the change is also a physical one. The water changes from liquid to solid, but it is still the same substance. That is why the freezing of anything is a physical change.

29．In a physical change ________ is formed.

A．a new substance B．nothing new

C．a piece of paper D．a piece of iron

30．The dissolving of salt in water is ________.

A．a physical change

B．a chemical change

C．hydrogen and oxygen

D．breaking up

31．The change of the three states of water is ________.

A．a chemical change

B．different substances

C．a physical change

D．the same state

32．We can separate a chemical change from a physical one by ________.

A．the change of shape

B．the change of color

C．newly­produced smoke

D．newly­formed substances