Highlight empty cell in column C once column A in same row has date entered

How can I highlight any empty cells in column C? I want these cells only to be highlighted if column A on the same row has a date input into the cell.

The spread sheet will be continually added to and I dont want any empty cells in column C that dont have a date in column A to be highlighted. Obviously once a date is added the empty cell will become highlighted until filled with data.

Hope that makes sense.

Im only just discovering the power of excel so have virtually no experience.