下列各句中，表达得体的一句是（ ）

Scientists think they have _____ in their attempt to find the causes of some major dieases.

What’s that on the desk —Oh, it’s ___________ old photo of my family .

I always had doubts he would be the best man for the job , but now I don’t doubt he can do it.

Nowadays school bus safety has drawn much attention nationwide for children’s safety is _______ worries parents most.