因租船订舱和装船而产生的单据是（）。 ["托运单","装货单","装箱单","海运提单"]
根据医疗器械缺陷的严重程度，医疗器械召回分为一、二、三级召回。三级召回是指（）。
《左传》
You have a DHCP server that runs windows server 2008. You restore the DHCP database by using a recent backup. You need to prevent DHCP clients from receiveing IP addresses that are currently in use on the network. What should you do?（） ["Add the DHCP serve option 44.","Set the conflict detetion value to 0.","Set the conflict detection value to 2."]
能引起土壤酸性的离子有（）。 ["H+<\/sup>","Ca2+<\/sup>","Mg2+<\/sup>","A13+<\/sup>","Na2+<\/sup>"]
试述动物传染病的预防措施。
