App responsive for screen (universal app-image resolution)

Hi, I want to know or it possible to create a program (via app inventor 2) which adjust to the device screen size (for multiple android phones and they screen sizes). 

One of the problem is the small screen on my device (LG L3 240 x 320 pixels, 3.2 inches) and as told for me SteveJG : "App Inventor 2 is designed for creating apps with a minimum screen size of 320 x 480."  but my device show  good programs in proportion to the screen with a resolution of ... I want to know most frequent android phone screen resolutions, that I could choose the most appropriate resolution (width height in pixels) for my app background images, to suit most Android phones and  do not distort background images and do not distort the whole app... How many it is advisable to choose the DPI (100-200)? What are options (ways) of making a program suitable for use with a different aspect ratio screens? And the best-accuracy emulator for test program for different screen sizes?

http://developer.android.com/guide/practices/screens_support.html#testing.  

I've said this before but you don't seem to be doing it... read my tips about the Emulators below:

For our App Inventor Tips, visit TwoDogApps.com

You can always use "Fill parent" sizes if it's simple.

Or, if you don't want strange stretching, you could do this:

When [screen].Initialize

    set [Image].Height to { [Screen].Width 

     set [Image].Width to { [Screen].Width  x [the image width/the image height]