#### Answer

$1-4=-3$
1 and 4 are natural numbers, but -3 is not.

#### Work Step by Step

Natural numbers are the counting numbers: 1, 2, 3, ...
The set of natural numbers is not closed with respect to subtraction, as can be seen in the example below:
1 and 4 are natural numbers.
However, $1-4 = -3$, which is not a natural number.