清晨，小鸟在树枝上发出悦耳的颤音。

In the morning, the little bird perched on the branch was ___trilling sweetly.

这位歌手正在练习如何在高音之间完美地颤音。

The singer is practicing how to perfect her ___trilling between high notes.

她在唱高音部分时，声音微微颤动着。

Her voice ___trilled slightly as she sang the high notes.