You copy the formula =sum($a1: c1) from cell d1 to cell f10. what will the formula change to?

The formula will change to =SUM($A10:E10)

Explanation:

Look at the difference between =SUM($A1:C1) and =SUM($A10:E10).

In both cases column A is present because in the original formula 'A' is next to '$' sign.

In the original formula the row 1 is used because the destination cell, D1, is in row 1; after the copy is made, the destination cell F10 is in row 10,  so the '1' is changed to a '10'.

C is changed to E because C column is the previous column to the destination cell, D1, in the original formula and E is the previous column to the destination cell, F10, after the copy.

answer; defense;