题目内容：

用所给词的适当形式填空

In many countries, ___1._____(smoke) is _2.__(become) a bigger problem for young people. Most smokers_3.__ (start) in their teens (years of a person's age from 13 to 19 ) or even earlier.

A study of 8,000 Beijing students last May4.___(show) us that smoking was a problem for many __5._(China) kids. More than 21% of middle school students and 6% of primary school _6._ (pupil) __7.__(say)they had smoked.

"If young people start_8. (smoke) early, they will probably get addicted to nicotine (对尼古丁上瘾).And it __9.__  (be) very hard to give up(放弃)_ 10.__( late) on," said a professor.