婴儿开始咿咿呀呀地发声了。

The baby started ___vocalising happily.

学生们在会议上大声表达了对校园安全的担忧。

The students were ___vocalising their concerns about campus safety during the meeting.

婴儿在三个月大时开始发出声音。

Babies begin ___vocalising around three months old.