我在听讲座时渐渐睡着了。

I ___drifted ___off while listening to the lecture.

飞机起飞后不久，他就渐渐睡着了。

He ___drifted ___off shortly after the airplane took off.

电影太无聊了，她看到一半就渐渐睡着了。

The movie was so boring that she ___drifted ___off halfway through.