[texhax] standard answer of a math paper

[Robin Fairbairns]

> Thanks for Philip and Douglas.
> 
> But I haven't find an answer yet.In amsmath packages,
> I tried almost all the align environments,but whenever
> I wrote my text in equation it would be looked as the
> part of the equation and be put in middle of the line
> together with the equation.And I can't find anything I
> need in the "exam.cls".

amsmath \intertext command gives you what you need.  as outlined in

http://www.tex.ac.uk/cgi-bin/texfaq2html?label=mathstext