在高等微积分讲座中，我感到完全力不从心。

During the advanced calculus lecture, I felt completely ___out ___of ___my ___depth.

在法律部门开始新工作时，面对复杂的案件文件，我立刻感到力不从心。

Starting my new job in the legal department, I was immediately ___out ___of ___my ___depth with the complex case files.

当被要求在没有管理经验的情况下领导这个项目时，他发现自己力不从心。

When asked to lead the project without any prior management experience, he found himself ___out ___of ___his ___depth.