What command is given to form a platoon at close interval?

The command "At Close Interval, Fall In" is the correct choice for forming a platoon at close interval. This specific command clearly instructs the members of the platoon to assemble in a tighter formation compared to the standard spacing used during normal intervals.

In military formation, a close interval is important for various purposes, such as maximizing the space efficiency in confined areas or maintaining unit cohesion during certain operations. The use of the phrasing "At Close Interval" directly conveys to the personnel that they should reduce the distance between themselves—bringing them closer together.

The other commands convey different assembly formations or intentions. For instance, "Fall In at Normal Interval" indicates that the personnel should stand at the standard distance apart, which does not achieve the objective of forming at close intervals. Similarly, "Close Ranks, Fall In" refers to a command used to close the ranks when troops are in a line, rather than forming the initial assembly. "Fall In Quickly" suggests a rapid gathering but lacks the specific instruction regarding the interval, leaving any intent for distance ambiguous. Thus, "At Close Interval, Fall In" is the most precise command for the formation described.