问题
选择题
— Could we practice playing the guitar in the hall, Sir ?
—No , ___________ you have the principal’s (校长) note.
A．if
B．unless
C．because
D．since
答案
答案：B
题目分析：句意：先生我们能在大厅练习弹钢琴吗？不行，除非你有校长的批条。A. if如果B. unless 除非，如果不C. because因为D. since自从……。根据句意，故选B。