The tough superficial layer of the epidermis is known as the stratum a) corneum. b) lucidum. c) basale. d) granulosum. e) spinosum.

Stratum corneum

Explanation:

Epidermis is known to be the outmost layer of the skin and it is made up of stratified squamous epithelium and keratinized.  Thus, stratum corneum is known to be the layer of the epidermis that is most superficial and that can be seen with our eyes. Furthermore, stratum corneum functions by preventing the dehydration of underlying tissues and microbes penetration

the sugar-phosphate backbone forms the structural framework of nucleic acids, including dna and rna. this backbone is composed of alternating sugar and phosphate groups, and defines directionality of the molecule.

i believe it would be c: tons.