The prefix con- means "with" or "together." For this reason, a group of people who are converging at the gate are coming together.
We can imagine a group of people spread out in a waiting lounge who come together at the gate in order to board a plane. Therefore, the correct answer is C.</span>
The best meaning of converge as it is used in the following sentence would be "come together" which is not only the best in this sentence but best in general.