If s, t and r are positive integers greater than 1, and s and t are factors of r, which of the following must be the factor of r^(st)?
I. s+t
II. t^s
III. s^2 * t^2 Select.
A) I only
B) II only
C) III only
D) I and II
E) II and III
given that s and t are factors of r.   so we can picture it this way r=s*t*n (n-some another factor of r)   so, r^st= (s*t*n)^st   I. s+t .since the question is MUST BE TRUE, we eleminate this option   II. (s*t*n)^st / t^s= integer YII and IIIS!   III.(s*t*n)^st/ s^2 * t^2 YII and IIIs, since we are said that integer s&gt;1 and integer t&gt;1
<result>E</result>
If s, t and r are positive integers greater than 1, and s and t are factors of r, which of the following must be the factor of r^(st)?
I. s+t
II. t^s
III. s^2 * t^2