How to include iOS SDK lower than 4.3 in Xcode 4.2

I just upgrade my Xcode to 4.2 because I upgraded my MacOS to Lion.

In this versi开发者_开发问答on of Xcode. only includes SDK 4.3, I can set the Deploy Target to 4.0 or other lower version, but different from old Xcode, I can't launched Simulators for lower SDKs.

I also tried download & install lower SDKs from old Xcode package, but seems it doesn't works.

So, in this situation, how I can publish app to support lower SDK devices?

THX~

Try opening XCode preferences, go to Downloads, and install the various debugging support options that are present.