Complex function/difference equation/integral transformation/stochastic process: If you study the content of time series, these four courses will be easier.
Matrix theory/real variable function/functional analysis: If you want to develop in an advanced direction, it will be better to have these three courses, because after learning these three courses, the world in your eyes will change, you can see what others can't see, and you can look at the problem from another angle.
[Before the weak crown, I was lost in the abstinence of econometrics; After that, reading econometrics books is as unimpeded as reading novels. At this point, I worked hard until I found myself going the wrong way]