单项选择题
What these young men were doing（）a threat to the safety of the whole neighborhood.
A.constructed B.contracted C.constituted D.contributed
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.
单项选择题 How to dispose （） the nuclear waste is a pressing problem for scientists and politicians alike.
