Var
  dc:set of char;
  s1,s2:string;
  i:integer;
begin
  dc:=['A'..'D','a'..'d'];
  s1:='То avoid the impression of the tail wagging the dog, '+
    'the president cannot be seen bending to the wishes of a minority.';
  s2:='';
  for i:=1 to length(s1) do
    if not(s1[i] in dc) then s2:=s2+s1[i];
  Writeln('Исходная строка: ',s1);
  s1:=s2;
  Writeln('Результирующая строка: ',s1)
end.

Тестовое решение:
Исходная строка: То avoid the impression of the tail wagging the dog, the president cannot be seen bending to the wishes of a minority.
Результирующая строка: То voi the impression of the til wgging the og, the presient nnot e seen ening to the wishes of  minority.