don not forget the lights when you leave.A 是to turn off B是turning off

don not forget the lights when you leave.A 是to turn off B是turning off
don not forget the lights when you leave.A 是to turn off B是turning off

don not forget the lights when you leave.A 是to turn off B是turning off
A

A

B是turning off,动名词

A to do 形式表示不要忘了做某事，该事还未做；doing表示忘了曾经做过某事。