The weights of 3 boxes are 4, 7 and 10 kilograms. Which of the following CANNOT be the total weight, in kilograms, of any combination of these boxes?

Correct option is D

Possible sums of selected boxes:
· 4 + 7 = 11
· 4 + 10 = 14
· 7 + 10 = 17
· 4 + 7 + 10 = 21
18 is not possible.