单项选择题
When she retired she did a lot of（）work for the Red Cross.
A.valid B.portable C.prosperous D.voluntary
单项选择题 What these young men were doing（）a threat to the safety of the whole neighborhood.
单项选择题 Doctors hope to（）a human heart into the patient within the next few days.
单项选择题 The tension（）as the guest of honor was about to announce the winner.
