A district and a state have the same sex ratio. Which of the following conclusions necessarily follows?

They share at least one demographic characteristic.

The correct answer is Option 3: They share at least one demographic characteristic.

A sex ratio is itself a demographic characteristic. If two populations have the same sex ratio, they necessarily share at least one demographic characteristic. Nothing can be concluded about age structure, dependency ratio, or overall population composition.

Option 1: Their population compositions are identical. Incorrect. Population composition includes many characteristics besides sex ratio.

Option 2: Their age structures are likely to be similar. Incorrect. Age structure cannot be inferred from sex ratio alone.

Option 3: They share at least one demographic characteristic. Correct. The sex ratio itself is a demographic characteristic.

Option 4: Their dependency ratios must be the same. Incorrect. Dependency ratio depends on age structure, not sex ratio alone.