很简单的问题，帮忙看一下(20分)

for t:=0 to 23 do
begin
if t<=5 then
begin
showmessage('a');
end
else if t>=6 and t<=11 then
begin
showmessage('b');
end
else if t>=12 and t<=17 then
begin
showmessage('c');
end
else
begin
showmessage('d');
end
end;
end;
上面语句错在哪儿？

for t:=0 to 23 do
begin
if t<=5 then
begin
showmessage('a');
end
else if (t>=6) and (t<=11) then
begin
showmessage('b');
end
else if (t>=12) and (t<=17) then//加括号
begin
showmessage('c');
end
else
begin
showmessage('d');
end
end;
end;

else if t>=6 and t<=11 then
~~
else if t>=12 and t<=17 then
这样写是错误的