Auto Sorting Column with Drop Down List in Cells

I have a Worksheet made of 4 Columns,120 rows, and headers in the first row. The fourth row is hidden and makes up the options for the drop down lists in each one of the cells in Column A. There are three options for the drop down lists that are text, and a fourth that is blank. I want to run a macro that will Alphanumerically Sort Columns A and B every time a value changes in Column A. Here's the kicker...values in A, B, and C have to stay paired next to each other. I have a Sort set up to do this, but can't record a macro that will run the sort every time a value is changed in Column A.