an后面加什么

　　He's an expert at getting his own way.

　　他在如何达到自己的目的方面很在行。

　　Lack of money will have an adverse effect on our research programme.

　　缺少资金将对我们的研究方案有不利影响。

　　It's an ideal proving ground for the new car.

　　这里是个理想的新车试验场。

　　Always make a backup disk as an insurance policy.

　　为保险起见，每次都要做备份磁盘。

　　There was so much traffic that we were an hour late.

　　路上车辆那么多，我们迟到了一个小时。