The exhaust ports of a diesel engine using the cross-flow scavenging method are opened and closed by the （） ["reciprocating motion of exhaust valves","rotary motion of the camshaft","reciprocating motion of the piston","developed differential"]
食人鱼是脂鲤目脂鲤科锯脂鲤属鱼类的统称，是南美洲食肉的海水鱼。
“昨日只是今日的记忆，明日只是今日的梦想”是谁说的？（） ["泰戈尔","波德莱尔","纪伯伦","安纳德"]
试述传染病的预防。
In a Cisco Unified Computing System， What is the "designated receiver" port in end-host mode used for？（） [" Sending all broadcasts"," Receiving all traffic from upstream switches"," Receiving broadcast traffic"," Negotiating spanning tree with upstream switches"," Learning MAC addresses from upstream switche"]
化学污染物的独立作用
