It was known that DNA had four chemical components - called adenine, guanine, cytosine, and thiamine - and that these paired up in particular ways.

当时已经知道，DNA含有4种化学成分——腺嘌呤、鸟嘌呤、胞嘧啶和胸腺嘧啶——这4种成分总是以特殊的配对方式排列。

DNA is made of four organic bases: adenine, guanine, cytosine, and thymine, or A, G, C, and T.

DNA 由四种有机碱基组成：腺嘌呤、鸟嘌呤、胞嘧啶和胸腺嘧啶，即 A、G、C 和 T。