DNA is a double stranded molecule made of nucleotides, while RNA is a single stranded molecule, also made of nucleotides.
Nucleotides are made of a nitrogen base, a phosphate and a sugar molecule (desoxyribose in DNA and ribose in RNA).
There are 5 nitrogen bases:
Adenin
Thymine
Guanine
Cytosine
Uracil
The DNA strands have the nitrogen bases Adenin, Thymine, Guanine and Cytosine, these bases pair together as follows:
Adenine = Thymine
Cytosine = Guanine
RNA also has 4 nitrogen bases, in this case, the base Thymine is replaced by the base Uracil, so the 4 nitrogen bases that form the strand are Adenine, Uracil, Guanine, and Cytosine. These bases form pairs as follows:
Adenine = Uracil
Cytosine = Guanine
For question 43, the correct answer is d. Thymine paris with adenine in DNA.