(1).in an experiment,they didn't notice me entering the room.( )
A.Engaging B.Having engaged
C.Engaged D.To be engaged
(2)--What do you enjoy most .in the summer holidays?
--Playing table tennis.( )
A.killing time B.to kill time
C.spendingthe time D.to spend the time
(3).with her son's progress in his studies,Mrs.Brown promised him a new CD the next day.( )
A.Satisfying B.To satiafy
C.Satisfied D.She was satisfied
(请说明选出选项的理由,)