A quiz appearing in a workbook for junior-high students of my country:<br/><br/>Fill in the blank with AN appropriate word:<br/><br/>Where are they playing tennis?<br/>- They are (........) in the park.<br/><br/>The answer booklet says "playing" is correct.<br/><br/>I think "playing" is INappropriate and appropriate is "doing", however.<br/>Advice would be appreciated.