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.
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