Final answer:
A 'cup' is a unit of liquid capacity equal to eight ounces or 0.25 liters, and the closest representation from the options provided is a cupped hand. It's larger than an eyedropper's volume but much smaller than a pool or bucket of water.
Step-by-step explanation:
One cup is a small customary unit for measuring liquid capacity. It is equivalent to eight ounces or about 0.25 liters. If we consider objects that might visually represent the size of a cup, a cupped hand is the closest match among the options provided. A pingpong ball is much smaller, a baseball is a bit smaller, a deck of cards is not of liquid measure, and a thumb is not comparable in volume to a cup.
For concept understanding, a cup as a unit of volume is smaller than units like a bucket of water or the water in a pool, but larger than a few drops from an eyedropper or the volume of a handful of rice. In the practice of comparison, one would need more cups to equal a pint, as a pint consists of two cups.