Why is it difficult for your body to return blood from your feet when you sit for too long?. Single choice. a. Blood has to travel a greater distance. B. Skeletal muscles are not squeezing the veins. c. Gravity makes the blood flow backward. d. The heart does not beat fast enough at rest.

Crinoids, also known as sea lilies, appear to be sea plants but are not plants at all. crinoids are an echinoderm species which uses anchoring structures called holdfasts to attach themselves to the sea floor. crinoids were most abundant in pennsylvania during the mississippian period, which ranged from 375 to 320 million years ago. fossils of the crinoids shows that during most of this time pennsylvania was that provided favorable conditions for crinoid growth. a) glacial terrain b) a dry and sandy plain c) mostly mountain ranges d) covered by warm, shallow seas