The sleep stage at which muscles begin to contract and relax is . A. Stage 1b. Stage 2c. Stage 3d. Stage 4 please select the best answer from the choices providedabcd.

Afish fossil is found in a rock. a foot bone and tooth are found in an older layer of the same rock. what can scientists learn from the rock? a) the area changed from land to water. b) the area changed from water to land. c) the area has always been land. d) the area was once an ocean.