The sequencing of the entire genome (the totality of all genes) of an organism was completed in 1996. The organism was

The first complete genome sequence of a eukaryote was the budding yeast Saccharomyces cerevisiae, released in 1996 as the result of a worldwide collaborative effort [1]. Authoritative summaries note that by May 1996 the S. cerevisiae reference genome — about 12 million base pairs across 16 chromosomes with ~6,000 genes — had been obtained and reported as the largest genome sequenced to that date [2]. The Saccharomyces Genome Database and original publications likewise record that the yeast genome was completely sequenced via international collaboration [3]. Therefore the correct answer is yeast (option 2); the other listed organisms were not the complete-genome milestone achieved in 1996.

Sources

1. [1] https://scholars.duke.edu/publication/1027368
2. [2] https://www.genome.gov/25520379/online-education-kit-1996-yeast-genome-sequenced
3. [3] https://www.yeastgenome.org/reference/S000086416