What key features do Web Scale infrastructure and applications share that contribute to their success?

What key features do Web Scale infrastructure and applications share that contribute to their success?
A . Intelligent hyper-optimized applications, clustered architecture, low OPEX, and HA design
B . HA design, distributed architecture, low OPEX, and design for failure
C . Clustered architecture, design for failure, HA design, and intelligent hyper-optimized applications
D . Design for failure, intelligent hyper-optimized applications, distributed architecture, and low OPEX

Answer: D.

Explanation: