What did Watson and Crick contribute to the discovery of DNA structure?

Watson and Crick are renowned for developing a model of DNA that revealed its double helix structure. This model was pivotal in understanding the molecular configuration of DNA, illustrating how the two strands coil around each other and how the base pairs (adenine with thymine and guanine with cytosine) are aligned. Their work provided insight into the mechanisms of genetic replication and the way information is stored and transmitted in living organisms, which has had profound implications for genetics and molecular biology.

In contrast, the other choices do not accurately represent Watson and Crick's contributions. They did not discover the structure of RNA; rather, their groundbreaking model was focused on DNA. They did not identify the function of ribosomes, which is related to protein synthesis but outside their primary research on DNA. Additionally, the first complete sequencing of the human genome was achieved much later, with significant advancements in technology and collaborative work beyond the contributions of Watson and Crick.