if I was taller.
Explanation:
since that's in the subjunctive mood, the right way to say it is:
"If I were taller, I could reach the top shelf "
or even better
If I were taller, I would reach the top shelf.
By the way, the verb create should be conjugated as :
"which word creates" with -es in the end of the verb.
I hope this helps you!
