工作票所列人员中，哪些人员不能兼职？
参考答案：工作票签发人不能兼任工作执行人，工作领导人、工作执行人均不能兼任许可人。
8分钟加工10个零件，平均每分钟加工______个，加工一个要______分钟．
When crossing a front,isobars tend to（）.
A.change from smooth curves within the air mass to sharp bends at the front
B.change from sharp bends within the air mass to smooth curves at the front
C.pass smoothly across the front with no change
D.become closer together at the front and pass through in straight lines
