A6 The histogram shows how many kilograms of muscle mass boys gained in one school year with regular visits to the fitness center. How many boys gained at least $2 \mathrm{~kg}$ of muscle mass?
(A) 2
(B) 3
(C) 4
(D) 5
(E) 11
A6 From the histogram, we read that four boys maintained their weight, five boys gained $1 \mathrm{~kg}$, two gained $2 \mathrm{~kg}$, and one gained $3 \mathrm{~kg}$. At least $2 \mathrm{~kg}$ was gained by three boys.