Explanation:

When comparing two quantities, it is important that they are in the same units. This allows us to properly assess the relationship between the quantities and determine which one is greater, smaller, or if they are equal.

Units:
- Units are a standardized way to measure and express quantities. They define the scale or magnitude of a particular quantity.
- For example, when measuring length, we use units such as centimeters, meters, or kilometers. In this case, if we want to compare the lengths of two objects, we need to ensure that both lengths are expressed in the same unit, such as centimeters or meters.

Comparing Quantities:
- When comparing quantities, we are essentially assessing their relative sizes or values.
- For example, if we have two lengths, one expressed in centimeters and the other in meters, we cannot directly compare them because they are in different units.
- However, if we convert both lengths to the same unit, such as centimeters or meters, we can then compare them and determine which one is larger or smaller.

Importance of Same Units:
- Having the same units allows for a fair and accurate comparison between quantities.
- If quantities are expressed in different units, it becomes challenging to assess their relative sizes.
- Without the same units, the comparison may be misleading and inaccurate.
- For example, comparing a distance in meters to a time in seconds does not provide meaningful information because these quantities have different units and cannot be directly compared.

Conclusion:
In order to compare two quantities, it is essential that they are expressed in the same units. This allows for a fair and accurate assessment of their relative sizes or values.