她在阳台上轻轻拨动吉他的琴弦。

She softly ___strummed the guitar strings on the balcony.

树枝敲打窗户发出轻轻的咚咚声。

The branches made a soft ___thump as they tapped against the window.

冰箱在夜里发出低沉的嗡嗡声。

The refrigerator ___hummed quietly during the night.