狒狒一道数学题 nn帮下忙

10、For all x, x is positive integer, "2-height" is defined
to be the greatest nonnegative n of x, what is the
greatest number of 2-height when 2" is the factor of x?
A. 2
B. 12
C. 40
D. 76
E. 90

答案是c 为什么啊 题目是啥意思啊?? nn解答下