For a scientific theory to be valid, which of the following must be true?

a. it must be well tested.
b. it must be widely accepted.
c. it must explain the observable facts.
d. all of the above

explain

For a scientific theory to be valid, it must be well tested, it must be widely accepted, and it must explain the observable facts. 
A scientific theory is confirmed through observation and are usually widely accepted. 

He was very egry and lowselfof steam