如何很好地对定义中的子项进行编号？

Question

我得到的代码：

\documentclass[a4paper]{article}
\usepackage{amsthm}

\begin{document}

\textbf{Definition 1.1} The definition contains following contents:
\begin{enumerate}
  \item The first item
  \item The second item
  \item This item may long enough to take up more than a line like this sentence. Line Breaking \ldots
\end{enumerate}

\end{document}

该代码的结果：

我想要的结果：

需要改变的内容：行间距、项目格式。

Answer 1

\documentclass[a4paper]{article}
\usepackage{amsthm}
\usepackage{enumitem}% http://ctan.org/pkg/enumitem

\theoremstyle{definition}
\newtheorem{definition}{Definition}[section]

\begin{document}
\setcounter{section}{1} % just for this MWE...
\begin{definition}
The definition contains following contents:
\begin{enumerate}[label=(\arabic*),leftmargin=2cm,itemsep=0ex,parsep=0ex]
  \item The first item
  \item The second item
  \item This item may long enough to take up more than a line like this sentence. Line Breaking \ldots
\end{enumerate}
\end{definition}

\end{document}

你可以考虑一下回答。