Which question cannot be answered by science?

why do rainbows appear after rain storms?
which plants grow in the desert?
why should endangered animals be protected?
what is the hardest element on earth?

Hi!

The question that science cannot answer is any question which is opinionated. It cannot have one true answer because it is simply subjective.

Other examples would be any question which cannot successfully follow the scientific method.

So, in the case of the question - the answer is going to be whichever question is opinionated. Just as a hint, not everyone thinks endangered animals should be protected. 

Hopefully, this helps! =)

The answer is b because a,c,and d are opinons