How to describe parts of equations underneath them? [duplicate]

Question

I want to describe parts of equation underneath them similar to this:

How do I go about doing this? I have the following code so far:

\begin{algin}
A = \frac{B}{C} + \frac{D}{E} + \frac{G}{H}
\end{align}

Answer 1

\documentclass{article}
\usepackage{amsmath}

\begin{document}
\begin{gather}
A = \underbrace{\frac{B}{C}}_{\substack{\text{comes}\\\text{from }X}} + 
    \underbrace{\frac{D}{E} + \frac{G}{H}}_{\substack{\text{comes}\\\text{from }Y}}
\end{gather}
\end{document}