Which of the following is a/are non-functional requirement of an e-learning system?

Which of the following is a/are non-functional requirement of an e-learning system?

(a) User friendliness
(b) Time taken to download study materials through the system should not be too long.
(c) On-line assignment submission facility
(d) On-line chatting facility
(e) Robustness

(a) User friendliness