if does not want to take "OR"?

I am confused now, I have the following simple script which reads 2 numbers from file test, and if any of these two numbers is bigger than 200, it prints biggest, bigger than 100, it prints medium, and smaller than 100, it prints "small number",

My question is, why if does not want to take this "-a" option?

I get the following error

"[: bb: integer expression expected"

#/bin/bash
while read aa bb
do

if [ "$aa" -gt "200" -a "bb" -gt "200" ];
then
echo "biggest"

elif [ "$aa" -gt "100" -a "bb" -gt "100" ];
then
echo "medium number"

else
echo "small number"

fi
done < /tmp/test

It should be $bb

haha, I can't believe I forgot the $ :):D:D:D