在挖掘作业时,挖掘松软土质时,铲斗角宜设定为()左右。
A.30°
B.60°
C.90°
D.120°
参考答案:B
A.Courses for doctors.
B.Courses for businessmen.
C.Courses for reporters.
D.Courses for lawyers.
承德原名热河上营,何时因何原因改为承德?