The pesticide ddt was widely used in the 1940s as a method of insect control. in the late 1950s the first ddt-resistant mosquitoes were discovered, and eventually ddt-resistant mosquitoes were found globally. when ddt is used now, the development of ddt resistance in mosquito populations occurs in months rather than years.

which of the following best explains the observations concerning ddt resistance in mosquitoes?
a. competition for limited resources causes mosquitoes to migrate to geographical areas that have richer supplies of ddt
b. the proportion of ddt-resistant mosquitoes in a population remains constant due to the metabolic costs of ddt utilization
c. natural selection favors ddt-resistant mosquitoes that are already present in a population when ddt exposure occurs
d. ddt is a chemical signal that delays normal reproductive cycles in many mosquito populations

On a backpacking trip, kenny hikes all day at a steady pace, covering 30 kilometers and burning 4000 calories. at the school track, janelle runs the 100-meter sprint in 13.5 seconds, burning 10 calories. afterward, janelle’s leg muscles are aching and she is breathing hard, while kenny maintains normal breathing all day, even though he burns 400 times more calories than janelle. which two statements offer the best explanation for this phenomenon? a. if the aerobic pathway—cellular respiration—cannot meet the energy demand, then the anaerobic pathway—lactic acid fermentation—starts up, resulting in lactic acid buildup and "oxygen debt." b. aerobic cellular respiration produces more energy, but its use is limited because of lactic acid buildup in the muscles and the resulting "oxygen debt." c. after about 90 seconds of intense exercise, the muscles become depleted of oxygen, and anaerobic respiration can no longer function to produce atp, resulting in "oxygen debt." d. the rate of energy demand determines how the muscles will obtain energy, either from cellular respiration or from lactic acid fermentation if not enough oxygen is present.