We can better define the problem by saying that solution is concentrated or diluted with respect to solution B or D respectively.
Concentration
The concentration of solution C lies somewhere between that of B and D.
Thus, if we are to qualify the concentration of solution C with respect to that of B, we will say it is concentrated.
If we are to qualify the concentration of solution C with respect to that of D, we will say solution C is diluted.
More on concentration can be found here: https://brainly.com/question/7127950