Deoxyribonucleic acid or DNA is a molecule composed of two chains of polynucleotides that match with each other.
Each nucleotide is formed by a phosphate group, a sugar called deoxyribose, and a nitrogen-containing nucleobase.
With the symbols of the question, each nucleotide would be as follows
The nucleobases form pairs, adenine (A) with thymine (T) and guanine (G) with cytosine (C).
In the diagram, you have one complete chain on the left and an incomplete one on the right:
Phosphate- Sugar - Adenine - Thymine - Sugar
Phosphate- Sugar -Thymine -Adenine- Sugar
Phosphate- Sugar -Guanine
Phosphate- Sugar -Cytosine
Phosphate- Sugar -Guanine
Phosphate- Sugar -Cytosine
Phosphate- Sugar -Thymine
So you would need to draw the missing part as follows:
Phosphate- Sugar - Adenine - Thymine - Sugar -Phosphate
Phosphate- Sugar -Thymine -Adenine- Sugar -Phosphate
Phosphate- Sugar -Guanine- Cytosine - Sugar -Phosphate
Phosphate- Sugar -Cytosine-Guanine- Sugar -Phosphate
Phosphate- Sugar -Guanine- Cytosine - Sugar -Phosphate
Phosphate- Sugar -Cytosine-Guanine- Sugar -Phosphate
Phosphate- Sugar -Thymine- Adenine- Sugar -Phosphate
Each pair should look like this: