16. In a mentoring program at a school, several first-grade students can become friends with one sixth-grade student, but a sixth-grade student cannot be friends with multiple first-grade students. It is known that $\frac{1}{3}$ of the sixth-grade students and $\frac{2}{5}$ of the first-grade students become friends. Then, the proportion of students who have friends among the first and sixth grades is ( ).
(A) $\frac{2}{15}$
(B) $\frac{4}{11}$
(C) $\frac{11}{30}$
(D) $\frac{3}{8}$
(E) $\frac{11}{15}$
16. B.

Let there be $x$ people in the first grade and $y$ people in the sixth grade. Then $\frac{1}{3} x=\frac{2}{5} y \Rightarrow x=\frac{6}{5} y$.

Thus, the required value is $\frac{\frac{1}{3} x+\frac{2}{5} y}{x+y}=\frac{4}{11}$.