What does A-20C stand for?

Apart from adenine (A), cytosine (C), guanine (G), thymine (T) and uracil (U), DNA and RNA also contain bases that have been modified after the nucleic acid chain has been formed. In DNA, the most common modified base is 5-methylcytosine (m5C). In RNA, there are many modified bases, including those contained in the nucleosides pseudouridine (?), dihydrouridine (D), inosine (I), and 7-methylguanosine (m7G).