My tags are follows:
\documentclass{book}
\usepackage{showframe}
\usepackage{gb4e,qtree,skull}
\begin{document}
\begin{exe}
\ex\emph{Superiority-obeying and Superiority-violating multiple
\emph{wh}-questions}
\begin{xlist}
\ex {\textit{Which} student read \textit{which} book? }
\ex {{\em Which} book did {\em which} student read ?}
\end{xlist}
\end{exe}
\end{document}
and the output came as:
How can I get the entries starts from the left margin, please advise...
