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I hate travelling by air __________ you usually have to wait for hours before the plane takes off.
A、because
B、though
C、until
D、unless
【正确答案】：A
【题目解析】：because因为；though 虽然，尽管；until直到；unless除非，如果不。句意：我讨厌乘飞机旅行，因为在飞机起飞前你必须等上几个小时。结合语境可知选A。