Laura added two three-digit positive integers. All six digits in these numbers are different. Laura’s sum is a three-digit number S. What is the smallest possible value for the sum of the digits of S ?

**Answer Choices**

A. 1

B. 4

C. 5

D. 15

E. 21

Laura added two three-digit positive integers. All six digits in these numbers are different. Laura’s sum is a three-digit number S. What is the smallest possible value for the sum of the digits of S ?

**Answer Choices**

A. 1

B. 4

C. 5

D. 15

E. 21