Hi,
You can do it with a formula like this
=INDIRECT(ADDRESS(5,ROW(A3)))
To be able to convert it to your needs you have to understand it. The first 5 is the row in which you have your first formula and the ROW(A3) bit is the column and ROW(A3) returns 3 so as posted the refers t row 5 and column 3 which is C5 and when you drag down it becomes D5.
Or another way which also starts on C5
=INDEX($5:$5,ROW(A3))