这次停电可能是由电线短路引起的。

The blackout ___may ___have been caused by a short circuit.

汤姆昨天可能没来开会；他身体不舒服。

Tom ___may ___not ___have attended the meeting yesterday; he wasn't feeling well.

到明年这个时候，他们可能已经完成了环球旅行。

By this time next year, they ___may ___have completed their round-the-world trip.