Select the most appropriate option to fill in the blank.

But if you ______ to spare before you do catch the bus, be sure to pop in.

have a moment

The most appropriate option to fill in the blank is have a moment.

The sentence is asking the person to stop by if they have a few minutes to spare before catching the bus. The word "moment" refers to a short period of time, which is what the person would have before catching the bus.

The other options are not as appropriate.

• Have a meeting refers to a scheduled gathering of people to discuss something. It does not make sense in the context of the sentence, because the person is not scheduled to have a meeting before catching the bus.
• Have a nap refers to a short sleep. It does not make sense in the context of the sentence, because the person is not going to sleep before catching the bus.
• Have a ride refers to a journey in a vehicle. It does not make sense in the context of the sentence, because the person is not going to take a ride before catching the bus.