AFTER THE INVENTION OF SPECIAL BREATHING EQUIPMENT, SCUBA-DIVING BE...

6. - DE KIEM TRA HOC KI 2 LICH SU
DE KIEM TRA HOC KI 2 LICH SU

6. After the invention of special breathing equipment, scuba-diving became a _____ sport.

A. uneasy B. healthy C. boring D. popular