Explanation:
A. Lets convert millimeters into kilometers.

since 4000000mm = 4km, A is true. (Not the answer)
B. Lets convert millimeters into centimeters.

Since 300mm > 3cm, B is true. (Not the answer)
C. Lets convert millimeters to meters.

Since 5m = 5000mm, C is NOT true. (Answer)
D.Lets convert metres to kilometres.

Since 2000m < 20km, D is true. (Not the Answer.)