Metagenomics Aims to Learn About the Diversity of Organisms, Particularly

Metagenomics aims to learn about the diversity of organisms, particularly microbes that inhabit natural environments. J. Craig Venter, a key figure in the race to obtain the human genome sequence, and his colleagues pioneered this approach in a study that analyzed DNA obtained from microbes collected from the Sargasso Sea, an intensively studied, nutrient-impoverished part of the Caribbean lying to the southeast of Bermuda. (C. J. Venter, K. Remington, J. F. Heidelberg, A. L. Halpern, D. Rusch, J. A. Eisen, D. Wu, I. Paulsen, K. E. Nelson, W. Nelson, D. E. Fouts, S. Levy, A. H. Knap, M. W. Lomas, K. Nealson, O. White, J. Peterson, J. Hoffman, R. Parsons, H. Baden-Tillson, C. Pfannkock, Y.-H. Rogers, and H. O. Smith. 2004. Environmental genome shotgun sequencing of the Sargasso Sea. Science 304:66-74.)
-Refer to the paragraph on the Venter et al. paper and the accompanying table. Because DNAs for sequencing were chosen at random with no way of knowing which organism they came from, how could genes be identified?

A) by searching for open reading frames (ORFs) , especially those with translation start and stop sites
B) by searching for similarity between predicted ORFs and those in existing databases
C) by searching for exons bounded by consensus donor and acceptor splice sites (those that mark exon/intron boundaries)
D) by searching for ORFs, particularly those with translation start and stop sites, as well as for similarity between predicted ORFs and those in existing databases