使用命令“\choice”删除多余的间距并改善间距

Question

\documentclass[12pt,a4paper]{article}
\usepackage[latin1]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{amsfonts,amsmath,amssymb,graphicx,amsthm,mathtools,systeme}
\usepackage[tikz]{bclogo}
\usepackage{pifont} %bouni
\usepackage{fancybox} %pour faire l'encadrement
\newcommand{\isEquivTo}[1]{\underset{#1}{\sim}}
%----------------------------debut multiple choice------------------
\usepackage{enumitem}
\usepackage{multicol}

\newlist{choices}{enumerate}{1}
\setlist[choices]{label*=(\alph*)}
\newcommand{\choice}{\item}

\SetEnumitemKey{twocol}{
  before=\raggedcolumns\begin{multicols}{2},
  after=\end{multicols}}

\SetEnumitemKey{threecol}{
  before=\raggedcolumns\begin{multicols}{3},
  after=\end{multicols}}

\SetEnumitemKey{fourcol}{
  before=\raggedcolumns\begin{multicols}{4},
  after=\end{multicols}}
%----------------------------Fin multiple choice------------------
\begin{document}
\noindent Choose the one correct answer by circling it below:
\begingroup % localize scope of the next two instructions
\addtolength\abovedisplayskip{-12pt}
\addtolength\belowdisplayskip{-12pt}
\begin{itemize}
\item[(1)] Determine the correct characteristic equation for the differential equation $y'' - 4y' + 4y = 0$.
\begin{choices}[twocol]
\choice $r^2 - 4r + 4 = 0$
\choice $r^2 + 4r + 4 = 0$
\choice $r^2 + 2r + 1 = 0$
\choice $r^2 - 2r + 1 = 0$
\end{choices}
  \item [(2)] State which of the following function is a solution of the differential equation: $y''-2y'+y=0$
\begin{choices}[twocol]
   \choice $y=1+e^x$
   \choice $y=xe^x$
   \choice $y=x+e^x$
   \choice $y=e^x$
\end{choices}
  \item [(3)] In the context of the differential equation $(E): y'' - 2y' + y = 5e^x$, a particular solution is in the form:
\begin{choices}[twocol]
   \choice $y_p=Ae^x$
   \choice $y_p=Axe^x$
   \choice $y_p=Ax^2e^x$
   \choice $y_p=A+e^x$.
\end{choices}
Here, $A$ is a nonzero constant.
\end{itemize}
\endgroup
\end{document} 

我想改善这里的间距。我尝试使用“\begingroup”，但没有看到任何变化。

Answer 1

我建议使用 ，tasks因为它更具可定制性（并保证同一行上的选项正确对齐，而 则不是这种情况multicol）。此外，阅读顺序也更自然。

\documentclass[12pt,a4paper]{article}
\usepackage[T1]{fontenc}

\usepackage{amsfonts,amsmath,amssymb,graphicx,amsthm,mathtools,systeme}
\usepackage[tikz]{bclogo}
\usepackage{pifont} %bouni
\usepackage{fancybox} %pour faire l'encadrement
%----------------------------debut multiple choice------------------
\usepackage{enumitem}
\usepackage{tasks}

\NewTasksEnvironment[
  label-width=20pt,
  label=(\alph*),
  before-skip=0.5\topsep,
  after-skip=0.5\topsep,
  after-item-skip=2\itemsep,
]{choices}[\choice]

\newcommand{\isEquivTo}[1]{\underset{#1}{\sim}}

%----------------------------Fin multiple choice------------------
\begin{document}

\noindent Choose the one correct answer by circling it below:

\begin{enumerate}[label=(\arabic*)]
\item Determine the correct characteristic equation for the 
  differential equation $y'' - 4y' + 4y = 0$.
\begin{choices}(2)
\choice $r^2 - 4r + 4 = 0$
\choice $r^2 + 4r + 4 = 0$
\choice $r^2 + 2r + 1 = 0$
\choice $r^2 - 2r + 1 = 0$
\end{choices}

\item State which of the following function is a solution
  of the differential equation: $y''-2y'+y=0$
\begin{choices}(2)
   \choice $y=1+e^x$
   \choice $y=xe^x$
   \choice $y=x+e^x$
   \choice $y=e^x$
\end{choices}

\item In the context of the differential equation 
  $(E): y'' - 2y' + y = 5e^x$, a particular solution is in the form:
\begin{choices}(4)
   \choice $y_p=Ae^x$
   \choice $y_p=Axe^x$
   \choice $y_p=Ax^2e^x$
   \choice $y_p=A+e^x$.
\end{choices}
Here, $A$ is a nonzero constant.
\end{enumerate}

\end{document}