桩机作业时，不得同时进行（）沉孔、压桩等两种及以上的机械动作。
A.吊桩
B.吊锤
C.回转
D.行走
参考答案：A, B, C, D
—I’ve got a new English teacher, Lucy Mere.
—Lucy Mere? She happens me before. She is patient.
A．to teach
B．teaching
C．to have taught
D．having taught
介绍要覆盖估算的流程？
