If m is an odd integer and n an even integer, which of the following is definitely odd?
+n)(m-n) b.. (m+n^2)+(m-n^2) c..m^2+mn+n^2 m+n

One way is to test it out with an odd and even integer
m=5 and n=4

A results in 14
B. results in 10
C, results in 61
D. results in 9

hmm, inspect last ones closely

let's see D
m+n
we know that even+1=odd
so
m=odd
n=even
m+n=odd+even=even+1+even=2even+1=odd

D is the answer