问题
选择题
All the guests at the party were dancing and singing happily _____ the electricity was cut off.
A．until
B．while
C．when
D．because
答案
答案：C
题目分析：句意：当电源被切断后，聚会上的所有客人都高兴地又唱又跳。Until直到；while然而；when当……时候；because因为，选C。