Smoking is one of the ______ causes of cancer, killing millions of people each year.[ ]

An earthquake killed over fifty people in this area, ______ hundreds of people homeless.

_____ the Internet is of greathelp, I don’t think it’s a good idea to spend too much time on it.

It is uncertain ________ side effect the medicine will bring about, although about two thousand patients have taken it.(2010·浙江)

What’s this inEnglish —It’s __________ .