Answer: The correct answer is- A) Rat.
R selected species are those species that can survive in unstable, unpredictable environmental conditions and produce large number of small size offspring ( with low survival rate and no parental care).
These species grow very rapidly and attain reproductive maturity at early stage in their lives.
Example- Insects, rats.
On the contrary, B) , C), and D) are K selected species that survive under stable environmental conditions and produce large size offspring with very few number ( having long life span and parental care).