他的个性是达成协议的主要障碍。

His personality is a major ___block to reaching an agreement.

缺乏资金一直是主要的绊脚石。

Lack of money has been the main stumbling ___block.

学生经常被要求展示某个主题，但主要的障碍是他们没有被给予如何正确做的知识。

Very often students are asked to present a certain subject, but the main stumbling ___block is that they are not given the knowledge of how to do it properly.