The inequality that must be true about the lengths of these segments is: CD < BC.
How to interpret the line segment division?
The segment addition postulate states that if B is a point on a line segment AC, then the sum of the lengths of AB and BC is equal to the length of the entire segment AC.
In formula form, it can be expressed as AB + BC = AC.
There are many different arrangements of points that satisfy the conditions. But, in all of these, the order of points starting from point A is A, B, D, C.
Because D is between C and B, distance CD is always shorter than distance BC. So, CD < BC.