#### Answer

I is the converse of II because the hypothesis and conclusion are swapped.
Inverse: If a, b, c and d do not form a 2-by-2 calendar square, then $a+d\ne b+c$.
Contrapositive: If $a+d\ne b+c$, then a, b, c and d do not form a 2-by-2 calendar square.

#### Work Step by Step

The inverse negates the hypothesis and conclusion.
The contrapositive both negates and swaps the hypothesis and conclusion.