Most text editors allow you to type return
(``enter'' on some computers), one or more spaces, then return.
TEX will not interpret the result as a blank line for
the purposes of ending answers. The file has to contain two
returns in a row without any intervening spaces. If in your
printout you discover than an answer has swallowed the following
exercise (or more), this may be the reason. Blanks are inserted
between returns by some word processors or editors, and
sometimes (apparently) by e-mail systems.
Many text editors allow you to detect blanks because the cursor
changes shape on a blank. Your editor may allow you to search
for the sequence carriage return, blank(s), carriage return, and
change such sequences globally to carriage return, carriage
return.