The correct answer is: a) Dhol.
The dhol is a double-headed drum that is used in a variety of musical genres, including Bihu music. It is a traditional instrument in Assam, India, and is often used in folk music and dance performances. The dhol is made of wood and has a skin on each head. The skin is usually made of goat or buffalo hide, and is stretched over the drum with a series of ropes. The dhol is played with two sticks, and the player can produce a variety of sounds by striking the drum in different places. The dhol is an important part of Assamese culture, and is often used to celebrate festivals and other special occasions.
The other options are incorrect because they are not traditional Assamese drums. The khol is a drum that is used in Indian classical music, the tabla is a pair of drums that are used in Indian classical music, and the mridangam is a drum that is used in Carnatic music.