Where did Gautam Buddha deliver his first Sermon ?

The correct answer is (a) Sarnath.

Gautama Buddha delivered his first sermon, the Dhammacakkappavattana Sutta, at Sarnath, a deer park near Varanasi in India. This sermon is considered to be the beginning of Buddhism.

Bodh Gaya is the place where Gautama Buddha attained enlightenment. Kushinagar is the place where Gautama Buddha died. Rajgrih is a city in India that was once the capital of the Magadha kingdom.