Which of the following CANNOT be weighed using a balance scale and these unit weights: 1, 4, 7, and 10  Choose the correct choice from the following answers:  A) 14  B) 15  C) 17  D) 21  E) 20
A. 13 (can be weighed by keeping weights of 10 and 4)   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. 21 (can be weighed by keeping weights of 10, 7 and 4 kg)   E. 19(cannot be weighed)   20
<result>E</result>
Which of the following CANNOT be weighed using a balance scale and these unit weights: 1, 4, 7, and 10