（）of the following messages is allowed to be transmitted on the radiotelephone without the authority of the Master. ["Urgency signal","Safety signal","Distress signal","None of the above"]
反映美国证券市场运行情况的主要股价指数包括（）。 ["道·琼斯指数","NASDAQ指数","《金融时报》指数","DAX指数"]
入驻青岛留学回国人员创业园需要具备什么条件？
MV SUDAN/MEAN AT 0200UTC IN POSITION 40.44N 141.52E PASSED A DERELICT ABOUT 40 TONS HALF SUBMERGED AND IS DRIFTING. This cable says that she met with possibly（）. ["a floating wreck","a survivor at sea","a man who had fallen overboard","a drilling rig"]
You hear on the radiotelephone the word SECURITE spoken three times. This indicates that（）. ["a message about the safety of navigation will follow","a message of an urgent nature about the safety of a ship will follow","the sender is in distress and requests immediate assistance","you should secure your radiotelephone"]
什么是助磨剂？对助磨剂有什么要求？简述助磨剂的助磨机理。
