The noun "hair" is uncountable, so it does not take a plural form like "hairs."
The correct structure for adjectives is: adjective + adjective + noun.
The correct phrase is:
"long and black hair".
The correct sentence should be:
"She has long and black hair."
Thus, the correct answer is Option A ("long and black hair").
Among scientists, the discovery of the double helix structure of DNA and the genetic code it incorporates is widely regarded to be one of the most significant scientific discovery of the twentieth century.