Which of the following Jaq operators groups one or more arrays based on key values and applies an aggregate expression?

A. join

B. group

C. expand
D. transform

Reference: https://books.google.com.pk/books?id=Qj-5BQAAQBAJ&pg=PA174&lpg=PA174&dq=Jaq+operators+groups+one+or+more+arrays+based+on+key+values+and+applies+an+aggregate+expression&source=bl&ots=zobr8AZzWy&sig=ZRCIH9ee4Un3Aam1hX8TzxfrfQI&hl=en&sa=X&redir_esc=y#v=onepage&q=Jaq%20operators%20groups%20one%20or%20more%20arrays%20based%20on%20key%20values%20and%20applies%20an%20aggregate%20expression&f=false