has been to是什么时态

The effect of the continuous attacks has been to wear out his troops.

接连不断的`攻击就是要拖垮他的军队。

Our policy has been to uphold the law

拥护法律是我们一贯的方针。

The Australian government's answer to the problem has been to throw money at it.

澳大利亚政府对这个问题的解决方案一直就是大把往里扔钱。

The effect of this has been to increasingly marginalize the local authority sector

这件事的影响是使地方当局越来越受到排斥。

The technique has been to mutate the genes by irradiation or chemicals

该技术是通过放射线照射或者使用化学方法使基因变异。