Answer:

Step-by-step explanation:
First of all, we have to define what refers "closed under addition".
The closure property under operations is when we operate to number and we get a result that's inside the same number field. For example, if we sum one integer with another one, we would have an integer as a result, that means integers are closed under addition.
So, if you observe the possible answers, you would see that
is not showing closure under addition, because it doesn't result in a irrational as the third choice do 
Therefore, the answer is the first option.