Don't let the graphical layout of the molecule deceive you! There are no branches in the carbon chain. (That is, no carbon atom is bound to more than two carbon atoms.) The molecule ethane is not called "methylmethane", so calling your molecule a methylpentane derivative would similarly be an error.
With no branches (and no rings and no double bonds etc.), and with six carbon atoms, we must be dealing with a hexane derivative. Once you know that, you just need to apply IUPAC rules that minimize the numbering of atoms to which substituents are bound. So answer B makes more sense than C, for that reason.