城市向郊区的扩张导致交通变得更加拥堵。

The ___expansion of the city into suburbs has caused more traffic congestion.

学校的新教学楼是对原有校园的扩建，增加了更多教室。

The new teaching building is an ___expansion of the campus to provide more classrooms.

社交媒体的扩张使全球文化交流变得更加便捷。

The ___expansion of social media has made global cultural exchange much easier.

在代数课上，我们练习了多项式的展开。

In algebra class, we practiced the ___expansion of polynomials.