Explanation:

- Head Count Ratio: This measures the percentage of the population living below the poverty line. It is a simple way to assess poverty by counting individuals who earn less than a specific income threshold.

- Poverty Incidence Ratio: This is another term for the Head Count Ratio. It also refers to the proportion of the population that falls below the poverty line.

- Both terms, Head Count Ratio and Poverty Incidence Ratio, can be used interchangeably as they describe the same concept.

- None of these options would be incorrect as both Option 1 and Option 2 are correct descriptions of the percentage of people below the poverty line.

Correct Answer: Option 3 - Both a and b