描述列表 - style=nextline 不起作用？

Question

\documentclass{article}
%% \documentclass[12pt, a4paper, UTF8, scheme = plain]{article}
\usepackage{amsmath}
\usepackage{enumitem}
\setlist[description]{style=nextline}
\begin{document}
\begin{description}%%[style=nextline]
\item[Exact answer $2.345 \pi$]
    \begin{itemize}
    \item Unless question is set in context (where some appreciation of appropriate accuracy is required),
    \item allow \textbf{A1} for $2.345 \pi$ on the answer line,
    \item allow \textbf{A0} for $2.35  \pi$
    \item Mark scheme will indicate in final column if marks to be allowed.
    \end{itemize}
\item[Exact answer $\sqrt{23}$]
    \begin{itemize}
    \item Scores \textbf{A1} if the question is not set in context and the $\sqrt{\text{prime number}}$ is given on the answer line.
    \item Scores \textbf{A0} if the question is set in context (where some appreciation of appropriate accuracy is required).
    \item Surd answers which simplify need not be simplified e.g. $\sqrt{12}$ or $2\sqrt{3}$ are acceptable but not irrational denominators -- if simplified, mark the simplified answer i.e. not isw
    \item Mark scheme will indicate in final column if marks to be allowed.
    \end{itemize}
\end{description}
\end{document}

为什么不从新行开始？