下列各句中，没有语病的一句是（ ）

______ some problems have arisen in the process, we are confident that we can handle them

I am going to take part in the 800-meter race this Friday.–____.

Why are so many northern Chinese visiting Southeast Asia countries recently ?—They are trying to get a ___shelter from the cold weather in winter.

Scientists warn us _____ the need tokeep an eye ____ the greenhouse effect.