Drop down list with criteria, please help!

Hello,

I have absolutely no idea on how to get the following to work on excel, please help!!!

1. A drop down list is created on Cell 1, with information A, B, C and D
2. A is selected in Cell 1, the cell next to cell 1 (collectively Cell 2) will have another drop down list with a set of dedicated data for further selection
3. When selection in Cell 1 has change to let say B, The source for drop down list in cell 2 should change to another set of data.

thanks a million in advance!!!