Concept:A valid Excel range must use column letters before row numbers, separated by a colon.Explanation:Option A: =SUM(10A:A17) is invalid because “10A” is not a valid cell reference.Option B: =SUM(10A:17A) is invalid because “10A” and “17A” are not valid cell references.Option C: =SUM(A10:A17) is valid because it refers to cells from A10 to A17.Option D: =SUM(A10:17A) is invalid because “17A” is not a valid cell reference.Answer:C. =SUM(A10:A17)