Complex sentence: Among ordinary-level candidates, 13.3 percent received an A-grade, and 66.6 percent received a C-grade or higher, but 21.5 percent received a D-grade and 11.9 percent failed.
Split into simpler sentences: Among ordinary-level candidates, 13.3 percent received an A-grade, with 66.6 percent receiving a C-grade or higher. However, 21.5 percent of ordinary-level candidates received a D-grade and 11.9 percent failed.