The best answer is D. i. and ii. only.
The Aswan High Dam generates electricity used by millions (i) and controls floods, reducing damage to farmland (ii). However, it is important to note that while silt is indeed not carried downstream as it previously was (iii), this is generally viewed as a negative consequence since the silt is important for maintaining soil fertility in the Nile Delta. Thus, iii is not considered a benefit.