单项选择题

A.腺嘌呤和胸腺嘧啶含量占20%
B.腺嘌呤和胸腺嘧啶含量占60%
C.鸟嘌呤和胞嘧啶含量占30%
D.鸟嘌呤和胞嘧啶含量占50%
E.鸟嘌呤和胞嘧啶含量占70%