他拒绝谈话是实现和平的主要障碍。

His refusal to talk is the main ___obstacle to peace.

这对许多年轻人来说可能是一个障碍。

This can be an ___obstacle for a lot of young people.

资金短缺是科学研究的主要障碍。

Lack of funding is a major ___obstacle to scientific research.