HCD (3ALPHA,8ALPHA)-CHOLEST-5-ENE-3,20-DIOL 20S-HYDROXYCHOLESTEROL C27 H46 O2 is hydroxyl at 20 C Back to the tutorial. 
The  27 carbon steroid and the  four rings of the steroid are labeled A,B,C and D. 
The methyl groups labeled 18 and 19  are called angular methyl groups -CH3 and 
double bond >C=C< between carbon atoms 5 and 6 and alcohol at carbon 3 and 20. 
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