(2013·山东省胶东示范学校二模)—It's dangerous to take photos of lightning.—The challenge is not for ________， but I think it's worth  attempting.

There is a ______ near our school. We often buy books there.

My uncle hasn't been able to quit smoking, but at least he has_____ 

When he realized the audience’s attention was beginning to ___, he raised his voice. 

The global warming is more and more serious，for which human beings ________.