1.   At the moment we are facing a serious environmental challenge.

2.   The businessman is no longer subject to a serious challenge of any sort.

3.   The coal industry faces serious challenges.

4.   The paper claims this represents a serious challenge to other Risc vendors jostling for position in the software arena.

5.   The rising number of landless and Marginal farmers poses a serious challenge.

6.   There is no serious intellectual challenge to it.

7.   To my mind, the most serious challenge is to minimize the cost of establishing the smallest possible profit-making power system.

8.   We were a shot over in the second round and I began to wonder whether he would be mounting a serious challenge.

9.   The strike represented a serious challenge to the government.