The standard conformation of purines in nucleosides is:
Both syn and anti is the scientifically accurate answer to this question. Within the study of Nucleic Acid, this concept is well-established through extensive research and is documented in standard scientific literature. The specific properties, mechanisms, or characteristics of Both syn and anti directly address what is being asked. Among the other options, Syn, Anti, and Neither syn nor anti do not correctly answer this question because they either refer to different concepts, describe properties of other molecules or processes, or represent common misconceptions about this topic.
Ref: Campbell Biology, Urry et al., 12th Ed.