There are two sets of parallel lines, their equations being `x cos alpha+y sin alpha=p` and `x sin alpha- y cos alpha=p` , `p=1,2,3,….n` and `alpha in (0,pi//2)`. If the number of rectangles formed by these two sets of lines is `225`, then the value of `n` is equals to
A. `4`
B. `5`
C. `6`
D. `7`