Question

what are the three main components of a dna molecule?
a. a sugar, a water molecule, and a nitrogenous base
b. a sugar, a phosphate group, and a nitrogenous base
c. a sugar, a phosphate group, and an amino acid
d. a sugar, a nucleotide, and an amino acid

Explanation:

DNA分子由脱氧核糖（sugar）、磷酸基团（phosphate group）和含氮碱基（nitrogenous base）组成。A选项中的水分子不是DNA组成部分；C和D选项中的氨基酸是蛋白质的基本组成单位，不是DNA的组成部分。

Answer:

B. a sugar, a phosphate group, and a nitrogenous base