<p>If k is a positive integer, let "K in a box" be defined as the set of all multiples of k. All of the numbers in which of the following sets are also in all three of the sets "2 in a box", "3 in a box", and "5 in a box"?</p>
<p>A. "5 in a box"
B. "6 in a box"
C. "10 in a box"
D. "21 in a box"
E. "60 in a box"</p>
<p>So um...yeah...what does this mean in English?</p>