In the Experiments of Liu and Colleagues, Mice Were Genetically

In the experiments of Liu and colleagues, mice were genetically modified so that active neurons in the dentate gyrus (DG) produced channelrhodopsin, a protein that would excite those cells when exposed to blue light. The rats were then subjected to fear conditioning and were observed to give a fear response (freezing) in the aversive environment. When they were tested in a familiar, nonthreatening environment, these mice

A) froze when the DG neurons were activated by blue light.
B) froze at all times.
C) did not show any fear responses when DG neurons were activated by blue light.
D) never froze.