Jasper has put up no parking signs outside his gate,but these have not had any effect.
问题描述：
Jasper has put up no parking signs outside his gate,but these have not had any effect.
为什么前后两句都用完成时.
答
“Jasper已经贴了禁止停车的标示”,用现在完成时,表示已经贴了,动作已经完成.
“但还是没用任何成效”,已经贴了,但是没成效,强调对现在造成的结果和影响.所以还是用了现在完成时.