18. The nitrogen base pairs for RNA are * O A. C-G AND A-T
O B. A-C AND T-U
C. A-U AND C-G
O D. C-G AND U-T

chordata is the answer

the principles and empirical processes of discovery and demonstration considered characteristic of or necessary for scientific investigation, generally involving the observation of phenomena, the formulation of a hypothesis concerning the phenomena, experimentation to test the hypothesis, and development of a conclusion that confirms, rejects, or modifies the hypothesis.