我答应和贝丝一起去派对，我觉得我不能让她失望。

I've promised to go to the party with Beth and I feel I can't ___let her ___down.

我向你保证我不会让你失望。

I promise you that I am not going to ___let you ___down.

经理向我们保证他会完成项目，但他错过了截止日期，让整个团队失望了。

The manager assured us he would complete the project, but he ___let ___down the entire team by missing the deadline.