RNA Bases: Two Purines (Double Ring) and Two Pyrimidines (Single Ring)

Steps:

• Identify RNA's four nitrogenous bases: adenine (A), guanine (G), cytosine (C), uracil (U).
• Classify purines with double-ring structure: A and G (two bases).
• Classify pyrimidines with single-ring structure: C and U (two bases).
• Match statements to facts: 1 and 2 describe the two double-ring bases; 3 and 4 incorrectly claim three single-ring bases.

Why B is correct:

• RNA nucleotides incorporate two purine bases (A, G) with double-ring structures, as defined in molecular biology, aligning exactly with statements 1 and 2.

Why the others are wrong:

• A includes 3, but RNA has only two pyrimidine bases (C, U), not three.
• C includes 4, which overstates single-ring bases as three instead of two.
• D includes 3 and 4, both erroneous due to the incorrect count of pyrimidine bases.

Final answer: B