Help w/If Statement

Hello,

Let us say I have 3 columns, column A is home email, column B is work email, and column C is other email. On column D, I want to return the value of column B if data is available, if data is not available, then I want to see if there is data in column C, if there is data in column C then I want to return that value in column D, if there is no data in column C then I want to look for data in column A. If there is data in column A then I want to return that value in column D, if there is no data in column A then column D can return the value of None.

Hope someone can help me w/figuring out the correct formula.

Thank you.