What is a main factor slowing down the transition from DVB-S to DVB-S2?

A. The high cost of broadcasting in 3D-HDTV
B. The lack of availability of HDTV content
C. The need to replace or upgrade set-top boxes, or acquire TVs with DVB-S2 integrated tuners
D. The incompatibility of DVB-S2 with existing satellite infrastructure
Answer: 