Which of the following CANNOT be weighed using a balance scale and these unit weights: 1, 4, 7, and 10  Select the correct option:
A) 13
B) 15
C) 17
D) 19
E) 21
A. 13 (cannot be weighed)   B. 15 (can be weighed by keeping weights of 10,4 and 1 kg)   C. 17 (can be weighed by keeping weights of 10 and 7 kg)   D. 11(can be weighed by keeping weights of 10 and 1 kg)   E. 21 (can be weighed by keeping weights of 10, 7 and 4 kg)   13
<result>A</result>
Which of the following CANNOT be weighed using a balance scale and these unit weights: 1, 4, 7, and 10