What type of Dynamic Tag Management rule and condition allows the developer to track cart adds?

A developer needs to measure the number of times that a visitor adds a product to their shopping cart on an e-commerce site. The cart add functionality of the result in an error when the visitor pushes the ‘Add to Cart’ button if a quantity has not been entered.

What type of Dynamic Tag Management rule and condition allows the developer to track cart adds?
A . An Event rule that will fire whenever the submit event occurs
B . A Direct Call rule that occurs immediately after a product is added to a visitor’s cart
C . An Event rule that will fire on the click of the "Add to Cart" button
D . A Direct Call rule that is set to fire on the click of the "Add to Cart" button

Answer: A