--It is really fun to hike and I often go hiking in the forest.--But hiking alone in the forest ______ be very dangerous.

-Why ________ it rain at weekends?-Never mind, let’s watch TV at home.

(2013·长沙二模)—The research on the new flu virus vaccine is challenging  and demanding.Who do you think can do the job?—________ my students have a try?

 ---  ________ have you kept the book ? --- Since last Month. I ________ return it to the library today or I can’t borrow one next time. 

It _____ last night., because the ground is all wet