chemistry help! MCQ organic question?

Firstly, in the question, "manganite" should be "manganate" instead, "3-onepentanoicacid acid" should be "3-oxopentanoic acid" instead, and "2-onepropanoic acid" should be "2-oxopropanoic acid" instead.

Acidified potassium manganate(VII) is a strong oxidizing agent which break a C=C double bond, and the two bonding atoms of the C=C double bond will be oxidized to carbonyl group(s) or carboxyl group(s) depending on the structure.

A and B are cyclic alkenes. Therefore, when the C=C double bond of A or B is broken, the rings will be opened and only one product is formed, but NOT two as in the question. Hence, rule out A and B.

C and D are cyclic dienes. Therefore, when the two C=C double bonds are broken, two products are formed. Hence, both C and D may be possible answer.

Refer to the two equations below. Only 1-ethyl-3-methyl-1,3-cyclopentadiene (C) gives the two expected produces.

The answer: C. 1-ethyl-3-methyl-1,3-cyclopentadiene