Question

Elena___en la tienda A) estoy B) esta C) es D) son

Answer 1

B) esta. esta typically refers to describing something like location whereas es describes the person's attributes. (ie, esta would be used with "she is in the store" and es would be used with "she is cute"

Answer 2

Elena esta en la tienda.  
The other verb to be is estoy and would be used as follows:
Yo estoy en la tienda.