X and Y are positive integers. If X is a prime factor of Y^2 , which of the following MUST be true?  Pick one
A) X is even  B) X=Y^2  C) Y/X is even  D) X/Y is less than or equal to 1  E) X+1 is also a prime factor of Y^2
A. x is even --&gt; not necessarily true: x=3=odd x=3=odd and y=3y=3;   B. x=y^2 --&gt; never true, as x=primex=prime then it can not equal to square of another integer;   C. y/x is even --&gt; not necessarily true: if x=3x=3 and y=3y=3 then yx=1=odd yx=1=odd;   D. x/y is less than or equal to 1 --&gt; always true as shown above or by POE;   E. x+1 is also a prime factor of y^2 --&gt; not necessarily true: if x=2x=2 and y=2y=2 then x+1=3x+1=3 and 3 is not a factor of y2=4y2=4.   Answer: X/Y is less than or equal to 1.
<result>D</result>
X and Y are positive integers. If X is a prime factor of Y^2 , which of the following MUST be true?