请问下面的两个if....怎么连用才正确？？？
<%
if 条件１ then
if 条件2 then
%>
结果
<%else%>
<%else%>
另一种结果
<%end if%>
<%end if%>

if a="" then
if b="" then
Response.write("a is null,b is null too.")
else
Response.write("a is null,but b is not null.")
end if
else
if b="" then
Response.write("a is not null,b is null.")
else
Response.write("a is not null,but b is not null too.")
end if
end if