Honestly I think you should look the words up in a Spanish dictionary. If you don't have one go get one. Whatever you do don't use google translate. It doesn't translate exactly right. You can use google translate for reading something in Spanish but never to write something.
Answer:
The answer is b) gimnasio
Explanation:
I read all the stories - this is the correct answer. I swear
Yo estoy en la tienda. (present)
Yo estuve en la tienda. (past)
Yo voy a estar en la tienda. (future)
Puedes explicarlo mejor porfavor?