关于英语现在完成时方面的.
Having turned off the TV set,he began to go over his lessons.=After turning off the TV set,he began to go over his lessons.
第一句话为什么用having done?动作是在began之前不是应该用过去完成时吗?是不是由于在句首的原因?可我还是不懂为什么用having turned,明白人讲一下.