Answer:
1. Phosphate
2. Guanine
3. Deoxyribose sugar
4. Adenine
Explanation: Remember the base pairing rules: cytosine with guanine and adenine with thymine, so whenever there's cytosine, there's guanine, and vice versa (the rules are a little different with adenine and thymine in terms of RNA). In the phosphate-sugar backbone, the phosphate will always be on the outside, and the sugar will always be found attached to the nitrogenous base.
Hope this helps,
Lacia
