4. A box contains 28 red balls, 20 green balls, 
19 yellow balls, 13 blue balls, 11 white balls, and 9 black balls. To ensure that at least 15 balls of the same color can be drawn from the box, the box must contain at least ( ) balls.
(A) 75
(B) 76
(C) 79
(D) 84
(E) 91
4. B.

Consider the extreme case: after taking away 25 balls, the box is left with 14 red balls, 14 green balls, 14 yellow balls, 13 blue balls, 11 white balls, and 9 black balls, totaling 75, which does not meet the requirement.

Then, by adding one more ball, the box will ensure that at least 15 balls of the same color can be drawn. Therefore, the box must contain at least 76 balls.