Which one is purine base?A. UracilB. ThymineC. CytosineD. Guanine

The correct answer is D. Guanine.

Here's a detailed explanation:

Purine bases are one of the two types of nitrogenous bases found in nucleic acids (DNA and RNA). They are characterized by a double-ring structure. The two purine bases are adenine (A) and guanine (G).

Pyrimidine bases, in contrast, have a single-ring structure. The pyrimidine bases include cytosine (C), thymine (T), and uracil (U).

Now, let's look at the options:

A. Uracil is a pyrimidine base found in RNA, not a purine.
B. Thymine is a pyrimidine base found in DNA.
C. Cytosine is also a pyrimidine base found in both DNA and RNA.
D. Guanine is a purine base found in both DNA and RNA.
So, the purine base among the given options is guanine (D).