In each case, identify the rule of inference used.

(a) John is a math major. Therefore, John is either a math major or a physics major.

(b) Sarah is a biology major and a chemistry major. Therefore, Sarah is a chemistry major.

(c) If it is raining, then the pool is closed. It is raining. Therefore, the pool is closed.

(d) If it snows today, then the university will close. The university is not closed today. Therefore, it did not snow today.

(e) If I go swimming, then I will stay in the sun too long. If I stay in the sun too long, then I will sunburn. Therefore, if I go swimming, then I will sunburn