Select the correct indirect form of the given sentence.
Bhola said to his mother, "Why is this charcoal so black?"

A

Bhola asked his mother why that charcoal was so black.

B

Bhola asked his mother why this charcoal is so black.

C

Bhola told his mother why that charcoal was so black.

D

Bhola asked his mother why was that charcoal so black.