Refer to figure.
The pilot of an aircraft in this scenario knows that they are going to have to wait some time before landing, which usually means entering a holding pattern. In order to maximise the amount of fuel they have left at this point, the crew should slow down and fly the rest of the way at the best endurance speed. As they are only going to end up holding anyway, they might as well save some fuel in the cruise, and have to do less holding patterns later on.

This is assuming that they have already "joined the queue" at their destination airport, which is implied in the question.

The best endurance speed in a jet aircraft is the speed at which the engines need to produce the least thrust, as thrust is directly proportional to fuel flow, and we want to make our fuel flow the lowest it can be. The speed of minimum thrust required is the speed of least drag (as thrust directly opposed drag). We called this V_MD, for minimum drag speed, and it is the speed that aircraft fly in the holding pattern, and when it is time in the air that is most desirable, rather than distance gone.

It occurs at the bottom of the "total drag" curve as shown in the annex above, where the combination of induced and parasite drag equals the lowest value.

There is no point climbing up to the optimum altitude at this stage, as it is not an efficient use of fuel to climb just before descent. Also, that option is not correct because we do not care about maximum range now, only maximum endurance.