Only after finishing your homework can you watch TV. 解释如下:副词only置于句首， 强调方式状语、 条件状语、 地点状语、 时间状语等状语时， 主句要进行部分倒装。例如： Only in a big city was it possible to buy a new wheelchair. 只有在大城市里才能买到新轮椅。Only when we had studied the data again did we realize that there was a mistake. 只有当我们再次研究了这些数据的时候， 我们才意识到出了一个错。Only because there were some canceled bookings did he get some tickets in the end. 一些预订被取消了， 他才得以买到了几张票。注意： 如果放于句首的only所修饰的不是状语时， 该句不用倒装。例如： Only John can save me. 只有约翰能够救我。Only some of the children passed the examination. 只有几个孩子通过了考试。你出的题目里因为是时间状语after..所以要倒装。
