题目内容：

阅读下面短文，在空白处填入1个适当的单词或括号内单词的正确形式。

Why Does Rain Smell So Good?

Do you love the smell of rain? If so, you’re not alone.

1.(actual), some scientists believe that people got their love for the smell of rain from 2.(ancestor), who relied on wet weather for their survival.

But what makes rain smell so nice? There are several smells associated with rainfall that people find pleasing.

One of these smells 3.(call) “petrichor（尘土的味道）.” Petrichor, a term created in 1964 by two Australian scientists studying the smells of 4.(rain) weather, comes from some chemical reactions.

During dry periods some plants produce oils, and when it rains, these oils go into the air. Another reaction occurs when chemicals 5.(produce) by some bacteria are sent out. All of these chemicals combine to create the pleasant pertichor smell when rain hits 6. ground.

Another smell associated with rain is ozone（臭氧）. During a thunderstorm, lightning can split oxygen and another gad and 7.(it) in turn can combine into a new substance. This substance reacts with other chemicals to form ozone, 8. has a sharp smell.

When someone says he can smell rain coming, it may be that wind from an 9.(approach) storm has carried ozone down from the clouds and 10. the man’s nose.