Which of these can refer to a boy but not a girl? a. cantante b. bailarin c. atleta d. joven

Cantante = singer (masc. or fem.) - el cantante, la cantante
bailarín = dancer (masc.) - el bailarín
atleta = athelete (masc. or fem.) - el atleta, la atleta
joven = young / young person (masc. or fem.) - el joven, la joven

B. Bailarín can refer to a boy, but not a girl, because the feminine is bailarina. All the others can refer to both boy or girl. 

It is letter b
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