Best reagent for reducing a ketone in the presence of an alkene
The Clemmensen reduction is really only effective at reducing ketones to alkenes when one group is aromatic. Additionally, the Clemmensen reduction uses concentrated HCl, which might cause problems. Another functional group in your molecule, the tertiary alcohol, will be removed by HCl via an elimination reaction.

Choice (b) is the Wolff–Kishner reaction, which also converts ketones into alkenes. It requires strong base (not acid) and works on almost all ketones.

Choice (c) will react with the alkene also, and so cannot be correct.