(5) A B C D E  
(本题您已经做了,答案为"D",在此仅供复习用,不能再计分!)
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上式中,
A (x){[(y)P(x,y,f(x,y))]∨(u)Q(g(x,u),u)}  
  B (x){[(y)(z)P(x,y,z)]∨(u)(x)Q(x,u)}  
  C (x){[(y)(z)P(x,y,z)]∨(u)(x)Q(x,u)}  
  D P(x,y,f(x,y)) Q(g(x,u),u)  
  E P(x,y,f(x,y))∨Q(g(x,u),u)