Assertion: Semiconductors have -ve temperature co-efficient of resistance.

Reason: As temperature of a semiconductor increases, number density of charge carriers also increases.

(a) Both assertion and reason are correct, but reason is not proper explanation. 

(b) Both assertion and reason are correct and reason is proper explanation.

(c) Assertion is correct but reason is wrong. 

(d) Assertion is correct, and reason also is correct.