大部分战斗都集中在山区。

Most of the fighting was ___concentrated ___in the mountains.

研究设施主要集中在大学校园周围。

The research facilities are ___concentrated ___around the university campus.

该领域的投资高度集中在少数几家大公司上。

Investment in this sector is heavily ___concentrated ___on a few large companies.