Unless otherwise posted, the speed limit for driving in an alley is:

Answer: B — 15 mph

The correct speed limit for driving in an alley, unless otherwise posted, is 15 mph. This speed limit is set to ensure safety in areas where vehicles may encounter pedestrians, cyclists, or other drivers, as alleys are typically narrower and more congested than regular streets. Keeping the speed limit at 15 mph allows drivers to react quickly to any sudden obstacles or changes in the environment, promoting safer driving conditions for everyone involved. The other limits, while reasonable for certain types of roads, are not applicable in this case because they exceed the speed limit that is specifically designated for alleys, which emphasizes caution and awareness of the surroundings.