他低声说话，以免吵醒婴儿。

He spoke in a ___low voice to avoid waking the baby.

大提琴演奏了一个低沉音符，在大厅中回响。

The cello played a ___low note that resonated through the hall.

有人在黑暗中低声警告。

Someone whispered a ___low warning in the dark.