Sub Articulo 85.0

a) you need to start using latex2e instead of latex2.09.
b) the following works for me:
\documentclass[a4,12pt]{article}
\usepackage{setspace}% for ``double-spacing'', etc.
\begin{document}
% double space (actually one-and-a-half)
\onehalfspacing
Today is very sunny day. I want to go to picnic with my friends.
But It's very unlucky that my car is broken.
% normal space
\singlespacing
The reason why my car is broken is that it is rainy at yesterday's 
night. I left the windows of my car open all night.
\end{document}