我们在一个拥挤的房间里等待。

We waited in a ___densely packed room.

墨西哥城是世界上人口最密集的城市之一。

Mexico City is one of the most ___densely populated cities in the world.

生活在一个人口密集的地区可能很有挑战性。

Living in a ___densely populated area can be challenging.