A double-helix. I encountered this question in my school, I looked in my gradebook and say the same question. I hope this helped you out!! :)
Answer:
DNA structure DNA is made up of molecules called nucleotides. Each nucleotide contains a phosphate group, a sugar group and a nitrogen base. The four types of nitrogen bases are adenine (A), thymine (T), guanine (G) and cytosine (C).
Explanation:
The respiratory system consists of all the organs involved in breathing. These include the nose, pharynx, larynx, trachea, bronchi and lungs. ... The nose, pharynx, larynx, trachea and bronchi all work like a system of pipes through which the air is funnelled down into our lungs.
D. Organic compounds contain carbon and inorganic compounds do not.