气候恶劣或从事复杂作业时，发票人必须向工作领导人进行安全技术交底。
参考答案：对
在关系代数中，从两个关系的笛卡尔积中选取它们的属性或属性组间满足一定条件的元组的操作称为______连接。
If two sailing vessels are running free with the wind on the same side, which one must keep clear of the other?（）.
A.The one with the wind closest abeam
B.The one to windward
C.The one to leeward
D.The one that sounds the first whistle signal
