反馈的类型不包括（）
A.正面的反馈
B.建设性的反馈
C.负面的反馈
D.以上都不是
参考答案：C
After the new technique was introduced， the factory produced _______ tractors in 1988 as the year before.
A．as twice many
B．as many as
C．as twice as many
D．twice as many
当举高消防车的驾驶室前移下沉时，接近角不允许小于（）度。
A.14
B.16
C.18
D.20
