The correct spelling of the word is through.
Writing trough instead
of through was probably
not really a spelling error but a typing mistake or what we call a typo.
The letter h was omitted.
Because trough is a
real word, the spell check on the computer did not catch it. We can see that it
is very important to review or proofread our work very carefully because we can
not depend on the computer to find and correct all of our mistakes.
