function chk:boolean;
  var ch:char;
  begin
    if eoln then chk:=false
      else begin
        read(ch);
        if (ch in ['p'..'z']) then chk:=true
          else begin
            if ch='N' then
              chk:=chk
            else if ch in ['C','D','E','I'] then begin
              chk:=chk and chk;
            end else chk:=false;
          end;
      end;
  end;

begin
  while not eof do begin
    if (chk)and(eoln) then writeln('YES') else writeln('NO');
    readln;
  end;
end.

实在不明哪里有问题...
EOF也试过，空行也试过，结果还是wa...大牛可否解释一下？