Sentence:  When <WSD>Johnny</WSD> Mercer and Harold Arlen began their collaboration in 1940 , Mercer , like Arlen , had several substantial film songs to his credit , among them `` Hooray for Hollywood '' , `` Ride , Tenderfoot , Ride '' , `` Have You Got Any Castles , Baby ? '' 
Meaning of the word marked with <WSD> tags:  a human being