A city was to be built at sea,housing 30000 people.

问题描述:

A city was to be built at sea,housing 30000 people.
housing 30000 people.作什么成分?为什么house要用ing形式?
housing 30000 people修饰什么?

现在分词作伴随状态housing 30000 people修饰什么?A city