Which of the following is a step when checking the burst mode in the M16/A2 function check?

In the process of checking the burst mode on the M16/A2, holding the trigger while pulling the charging handle is a crucial step. This action ensures that the weapon is properly cycled while engaging the burst feature, allowing the weapon to function as designed in burst mode. By holding the trigger, the system can accurately assess whether the weapon will fire multiple rounds in succession as intended when in burst mode. This step is essential for confirming that the mechanism engages correctly and that the burst mode operates without failure.

While other options present various actions related to trigger control or mode selection, they do not specifically address the checking of the burst functionality in the manner prescribed for this weapon system. Hence, pulling the trigger twice, releasing the trigger after a single pull, or switching to the semi mode doesn't contribute directly to the verification of burst mode operational integrity.