The average of 20 numbers is zero. Of them, at the most, how many may be greater than zero?

A. 0
B. 1
C. 10
D. 19
Average of 20 numbers = 0
Sum of 20 numbers = (0 * 20) = 0
It is quite possible that 19 of these numbers may be positive and if their sum is a, then 20th number is (-a).