（对划线部分提问）David and Linda have been watching TV for four hours.（watching TV划线）David and Linda have been watching TV for four hours.（watching TV划线）_____ _____ David and Linda _____ _____ for four hours?
问题描述：
（对划线部分提问）David and Linda have been watching TV for four hours.（watching TV划线）
David and Linda have been watching TV for four hours.（watching TV划线）
_____ _____ David and Linda _____ _____ for four hours?
答
What have ……been doing