The underlined word" range" probably means ______.

A．people who are interested in something
B．people who are engaged in something for enjoyment and without being paid for it
C．people who are engaged in a specified activity as one's main paid occupation
D．people who are present

A．has been put into actual use
B．was put into actual use in 1977
C．was put on experiment in 1977
D．had been repeatedly experimented on before 1977