下列各句中，加点成语使用恰当的一句是：（ ）（3分）

Jimmy is very helpful. _____I stay with him, _____I like him.

y have missed the train, ______ she won’t arrivefor another hour.

_____ the steep mountains，he had no difficulty reaching the top.

With the help of high technology, more and more new substances ______ in the past years