Answer : 4. "Nematode"
Explanation :

The researchers found that the offspring of C. elegans worms, after ingesting disease-causing bacteria, inherited the knowledge from birth to avoid those same bacteria. C. elegans, a nematode worm, matures from egg to adult in 3–5 days, providing insights into human and biological science. It was the first multicellular organism whose genome sequence and nerve wiring were mapped.