UltimateTax uses line C for any royalty income from K-1 P/S (partner/shareholder) Worksheets. The form displays the words "FROM K-1" in the Address field when there is royalty income coming from one or more K-1 P/S Worksheets.
If the client has K-1s, fill in a K-1 worksheet for each before completing Schedule E.
If the client does not have K-1 income, you can use this line for a third property. However, you cannot link to Rental Worksheet for this line.