用括号中词的适当形式添单词；
It’s a good habit to brush ___________(tooth)three times a day.
If there are more trees on the earth, there will be ________(little) pollution.
I hope to finish __________(write) my first book by the end of the year.
Thanks for _______(give) me so much help with my English.
More natural reserves(保护区) will be _________(build) in our country in the next few years.