The answer is C.

Statement 1 just tells us that two adjacent internal angles are not identical within a quadrilateral.

Hence Statement 1 alone is INSUFFICIENT

Statement 2 alone tells you that it is a rhombus (a square is just a special case of a rhombus)

For a rhombus, the two diagonals are not of the same length unless it happens to also be a square.

Hence Statement 2 alone is INSUFFICIENT.

If you combine Statement 1 and 2 then you have a SUFFICIENT condition.

You know it's a rhombus, so the sides are equal length, and you know one angle is larger than the other.

Therefore you know that AC is the longer diagonal of the two. If this not obvious to you, draw it out on a piece of paper, and it'll immediately come to you.

If you want the mathematical explanation [WHICH IS NOT NECESSARY FOR DATA SUFFICIENCY], then you need to know the

cosine rule.

Using the cosine rule, we know that

|AC|^2 = |AB|^2 + |BC|^2 - 2|AB||BC|cos(angle ABC)

|BD|^2 = |BC|^2 + |CD|^2 - 2|BC||CD|cos(angle BCD)

Since it is a rhombus, |AC| = |BC| = |CD|, and we'll call this length x.

So |AC|^2 - |BD|^2 = 2(x^2)(cos(angle BCD) - cos(angle ABC))

angle (BCD) < angle (ABC), therefore cos(angle BCD) > cos(angle ABC)

Hence |AC|^2 - |BD|^2 > 0, so |AC| > |BD|