An earthworm is crawling along the pathway of a maze. Ammonia is sprayed onto its body, and that causes the earthworm to recoil all earthworms respond this way without any training or experience). A scent is sprayed at the earthworm and there is no reaction. However, the researcher sprays the rose scent, and then one second later sprays the ammonia, which causes the recoil reaction. Eventually the earthwortn recoils to the rose scent. NS?
US?
CS?
UR?
CR?