About 4,00 new species of marine animals were discovered in the last 2 years. What is the unit rate of discovery?
1 species/2,000 years
4,000 species/2 years
2 years/4,000 species
2,000 species/ 1 year
1 species/2,000 years
4,000 species/2 years
2 years/4,000 species
2,000 species/ 1 year