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

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