The aircraft on ground， engine not running， which hydraulic system can be used

题目解析 The aircraft on ground, engine not running, which hydraulic system can be used A. Yellow system only B. Yellow and blue system C. Yellow and green system D. Yellow, green and blue system 答案:D 解析：在飞机停在地面且发动机未运行时，可以使用黄、绿和蓝三个液压系统。选项D是正确答案。