Look out.Organic chemistry.(277)

Nice question...this is a pretty good one. Lots of concepts working together.

Is that a six membered ring in the starting?

No it is not the six membered ring.

OsO₄ --> Syn-di hydroxylation
NaIO₄ --> Oxidation of vicinal diols
OH^- --> Intramolecular aldol cyclization
NaOH(aq) --> S_N1 reaction as OAc is very good leaver.

I missed out a methyl group there...ans is D.

Don't flatter me bhai :P all of us can solve this if we break the problem and go at it one by one...agar main tumhe reagents ke purposes bata deta you would've arrived at the ans yourself! trust me.
I might be wrong also. We need more views on this question.