The correct answer is option 'D' (Both [b] and [c]).

Capacity refers to the amount of space that an object can hold or the amount of liquid that can be contained in a container. It is measured using different units depending on the quantity being measured. In this case, we are measuring the capacity of a container or object, so we use the unit of volume.

The unit used for measuring capacity can vary depending on the context and the country. However, the most commonly used units for measuring capacity are liters (L) and milliliters (mL).

Let's understand each unit in detail:

1. Liter (L):
- Liter is the primary unit used for measuring capacity and volume.
- It is a metric unit of measurement and is equal to 1000 milliliters.
- Liters are used to measure the capacity of larger containers or objects, such as bottles, tanks, and swimming pools.

2. Milliliter (mL):
- Milliliter is a sub-unit of the liter and is used to measure smaller quantities of liquid.
- It is equal to one-thousandth of a liter or 0.001 liters.
- Milliliters are used to measure the capacity of smaller containers, such as medicine bottles, drinking cups, and test tubes.

So, both liters and milliliters are used for measuring capacity, with liters being used for larger quantities and milliliters for smaller quantities.

In conclusion, the unit used for measuring capacity is either liters (L) or milliliters (mL), depending on the size of the container or object being measured. Therefore, the correct answer to the given question is option 'D' (Both [b] and [c]).