Is(are) described as slow-wave sleep.
stage 1
stage 2
stage 3 and stage 4
rem sleep

The form the boundary between north and south china. a. himalayan mountains c. change river b. xi river d. qinling shandi mountains

How have people adapted physically to different environments? why do you think these differences developed?

How did the percentage of americans living on farms change between 1820 and 1850 a. it lowered as many americans were sold into slavery b. it rated the same as people stopped coming to america c. it grew as more people came to america d. it lowered as many americans went to work in factories