Question

what does relative humidity measure?
the amount of water in cirrus clouds
the amount of water that has evaporated into the air
the amount of frozen water that has condensed from the air
the amount of water vapor in the air compared to the amount the air can hold

Explanation:

Relative humidity is a measure that compares the actual amount of water vapor present in the air to the maximum amount of water vapor the air can hold at a given temperature. It is not about water in specific clouds (like cirrus), just the amount evaporated (without the comparison), or frozen condensed water.

Answer:

the amount of water vapor in the air compared to the amount the air can hold