3. What is he ... ?

The correct answer is c) doing.

Explanation: The phrase "What is he ... ?" is a common structure to ask about someone's current activity. The verb that fits here is 'doing', forming the question 'What is he doing?'. The other options, 'does' and 'do', are forms of the auxiliary verb used in simple present or past tenses, not the present continuous which is implied by the structure.