If a is a rational number and b is an irrational number, then the sum a + b is

C: Irrational

Explanation:

the reason i chose C because when you add a rational and irrational number together you still get a repeating number which is irrational.

For Example: Take a rational number 5 and Pi

if you ad those together 5+3.1415... you still get a repeating decimal, and repeating decimals are also irrational numbers.

Hope this helps :D