许多泡泡聚集在一起。

Many bubbles are ___clustered together.

学生们在操场上三三两两地聚在一起。

The students ___clustered in small groups on the playground.

游客们聚集在广场上，形成密集的人群。

Tourists ___clustered in the square, forming dense crowds.

学生们把椅子聚在一起围成讨论圈。

The students ___clustered the chairs into discussion circles.