Science:Math Exam Resources/Courses/MATH102/December 2015/Question 08/Solution 1

If D increase and DM is a constant, then M should at least decrease. Now leaves us (c) and (d).

Suppose D=t, which satisfies the description "D increases at a constant rate",( you can also be more precise like D=D0 + at, but it is not necessary since we just wanna check if rate is constant).

Then "DM=C" becomes "tM=C", then "M=C/t", thus the derivative of M is not a constant.

answer: $\color {blue}(d)$