答案1
您可以使用该hf-tikz
包:
\documentclass{beamer}
\usepackage[beamer,customcolors]{hf-tikz}
\hfsetfillcolor{bg}
\hfsetbordercolor{red}
\begin{document}
\begin{frame}
\begin{align*}
E\left(Y_i(1)-Y_i(0)\right)&=E\left(Y(1)-Y(0)\right)
\\&= E(Y(1))-E(Y(0))
\\&\tikzmarkin<2->{a1}=\tikzmarkend{a1}E(Y|T=1)-E(Y|T=0)
\end{align*}
\end{frame}
\end{document}