\documentclass{article}
\usepackage{filecontents}
\begin{filecontents*}{packageA.sty}
\DeclareOption{opt}{\PassOptionsToPackage{opt}{packageB}}
\ProcessOptions
\RequirePackage{packageB}% Load packageB.sty
\end{filecontents*}
\begin{filecontents*}{packageB.sty}
\DeclareOption{opt}{\AtEndDocument{\texttt{opt} passed}}
\ProcessOptions
\end{filecontents*}

\usepackage[opt]{packageA}

\begin{document}
test
\end{document}