【C20】A．whileB．forC．afterD．until

【C20】A．beforeB．whenC．sinceD．until

【C20】A．onB．forC．uponD．at

Ms. Silva sent the memo ______ it had been approved.A．soB．butC．afterD．until

Young people tend to______disco because of its exciting rhythms.A．go inB．go forC．go afterD

It was not until 1920 ______ regular broadcast began.A、whileB、whichC、thatD、since

【C20】A．andB．forC．orD．then