Conditional Formatting: Duplicate rows based on multiple columns.

Hi all,
I do apologize if this has been asked and/or answered before, when I tried searching, all I got was thousands of entries that didn't seem to quite catch what I'm looking for.
I will try to explain this right: I'm looking for a Conditional Formatting formula that will check two columns before highlighting the duplicate rows. I need it to be conditional formatting because I know nothing about writing macros or vba (what-ever that is?).
Data is entered into Columns A, B, and C. I need to check both column A and C before it highlights the duplicates, based on those two columns. (The format only unique or duplicate values checks only one column.)
I have attached an example, but this is just an example, as I have hundreds of lines to go through on the original. (For this example, Row 2 and Row 7 are the duplicates I need highlighted.)

Any help would be appreciated. Thanks in advance.

Example.xlsx

That works great! Thank you very much.