%PsTricks content-type (pstricks.sty package needed)
%Add \usepackage{pstricks} in the preamble of your LaTeX file
\psset{xunit=1.5mm,yunit=1.5mm,runit=1.5mm}
\psset{linewidth=0.3,dotsep=1,hatchwidth=0.3,hatchsep=1.5,shadowsize=1}
\psset{dotsize=0.7 2.5,dotscale=1 1,fillcolor=black}
\begin{pspicture}(0,0)(58,47)
\rput{0}(10,45){\psellipse[fillstyle=solid](0,0)(2,-2)}
\rput{0}(50,45){\psellipse[fillstyle=solid](0,0)(2,-2)}
\rput{0}(10,5){\psellipse[fillstyle=solid](0,0)(2,-2)}
\rput{0}(50,5){\psellipse[fillstyle=solid](0,0)(2,-2)}
\rput(3,45){\Huge a}
\rput(58,45){\Huge b}
\rput(3,5){\Huge c}
\rput(58,5){\Huge d}
\psline(16,45)(46,45)
\psline(50,40)(50,11)
\psline(46,5)(16,5)
\psline(10,40)(10,11)
\psline(13,41)(44,10)
\end{pspicture}