MIk làm bài 4 thôi nha
4.
program Tin_hoc;
uses crt;
var i:integer;
s,s2:string;
begin
clrscr;
writrln('Nhap xau S:');readln(s);
s2:='em';
for i:= 1 to length(s) do if (s[i] = 'a') and (s[i+1] = 'n') and (s[i+2] = 'h') then
begin
delete(s,i,3);
insert(s2,s,i)
end;
writeln(s2);
readln;
end.