飞机着陆进近中，提醒放起落架的警告形式一般为：（）.
A.语音提示
B.断续喇叭响，绿色指示灯亮
C.连续喇叭响，红色警告灯亮
D.喇叭警告
参考答案：C
His grandpa _______ for 2 years.
A. has been died B. has died C. has been dead
沿齿轮任意圆周上，轮齿两侧渐开线间的弧长称为（）。
A.齿距
B.齿厚
C.齿宽
D.全齿高
