Provide the structural formula of cholesterol.

(N/A) Cholesterol is a type of lipid,specifically a sterol. Its chemical formula is $C_{27}H_{46}O$. Structurally,it consists of a tetracyclic cyclopenta[$a$]phenanthrene skeleton,which includes four fused rings: three six-membered rings $(A, B, C)$ and one five-membered ring $(D)$. It also features a hydroxyl group $(-OH)$ at the $C-3$ position,a double bond between $C-5$ and $C-6$,and an alkyl side chain at the $C-17$ position. The provided image illustrates this characteristic four-ring steroid backbone.