may have

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.

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.

英国科学家认为，他们可能已经找到一种对抗普通感冒的方法。

British scientists believe they ___may ___have found a way to fight the common cold.