B - not authentic; fake
Apocyphal is typically a story or statement that is false or made-up but widely believed to be true. 
 
        
             
        
        
        
Hello!
I believe your answer is B
Ultimately, he chose advertising, where he would learn about making commercials.
Finally and ultimately are very similar in definition.
A. does not make sense, because finally is longer, and briefly means shorter.
C. doesent work because chiefly means "for the most part", he fully decided on it.
D. does not work because moreover means "as a further matter" which doesent make sense in this case.
I hope this helps!
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King or Prophet
Hope this helps! Have a nice day!