Choose the correct word to complete the following sentance: a natural number is (always, sometimes, never) a whole number

A natural number is always a whole number

The set of natural numbers is this {1, 2, 3, 4, 5, ...} basically the set of counting numbers. Zero is not part of this set.

The set of whole numbers is {0, 1, 2, 3, 4, 5, ...} almost the same set but now zero is part of the group. 

Any number in the first set is automatically part of the second. We consider the first set to be a subset of the second set. Any natural number you can think of is also a whole number. The same cannot be said the other way around. As you can see, zero is NOT a natural number. So the set of whole numbers is not a subset of the natural numbers.