program t2;
var letter:char;
begin
for letter:='a' to 'z' do
if (ord(letter)-ord('a'))mod 2=0 then write(letter:3);
writeln;
for letter:='z' downto 'a' do
if (ord(letter)-ord('z'))mod 2 =0 then write(letter:3);
writeln;
end.
输出： a c e g i k m o q s u w y
z x v t r p n l j h f d b