Review the following graph:Graph labeled time on the x-axis and strength of CR on y-axis from weak to strong. The part of the wave labeled Acquisition and NS plus US rises from weak to strong as time passes. The next part of the wave labeled Extinction and CS alone decreases from strong to weak as time passes. After a break in the wave, the line begins again at moderate strength and is labeled Spontaneous recovery of CR. The wave then decreases again to weak and is labeled Extinction and CS alone.Based on the graph, which statement accurately describes acquisition and extinction? aThe strength of the response decreases and then increases over time. bThe strength of the response increases and then decreases over time. cThe strength of the response remains constant over time. dThe strength of the response increases at a constant rate over time. eThe strength of the response decreases at a constant rate over time.