In the study by Costello et al. (2014) where rats were trained to lever press for an i. v. infusion of nicotine, different results were observed when nicotine was delivered alone compared to when the nicotine was a component of cigarette smoke extract (CSE). What did they find in rats lever pressing for CSE compared to those responding for nicotine alone

Ascientist observes certain changes in the physical features of a particular species over time. she concludes that the species has undergone evolutionary change. she wants to study the animals by analyzing their population. she’ll use . the population of this species is decreasing considerably. if this trend doesn’t change, this species will fall under the category of animals. this is a plato question,i need to make up his biology credit.