Answer:
D. 11 < x < 19.
Explanation:
The third side x is between 11 and 19 cm.
Consider sides AB (length 4) and BC (length 15) of the triangle.
Consider the angle between AB and BC is slightly less than 180 degrees. To get from point A to point C, we have to travel almost the entire length of A to C, which is from A to B and then B to C, so a bit less than 19 cm.
Consider the angle between AB and BC is slightly more than 0 degrees. To get from point A to point C, we subtract the length of AB (because we're already further along BC), so 15 - 4, a bit greater than 11.