Apply coupon code only for specific category

Question

I am working on magento 1.9.1.

I am offering 50 % off if customer add product to cart from particular category (Say Category A).

In the cart page, the customer have added other category products too.

Ex:

Product 1 - Category A, Product 2 - Category C, Product 3 - Category B

When we apply coupon code, its applying for all products in cart.

But, the coupon must not apply if Other category products are added (Say Category B & C).

Answer 1

Duplicate the conditions into the "Apply the rile to cart items matching....".
it clearly states in the title "leave blank for all items".