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

In  order for a scientific theory to be valid, it must be testable. that's true but current physicists are using the non-testable nature of sub atomic particles and matter/energy to put forward crackpot theories based on nothing but ideas and guesswork, global warming is another example, unreliable data being interpreted to match the theory that doesn't stand up to rigorous examination but anyone doing that is immediately demonized and ridiculed

should be cytoplasm or cell membrane