Why are enhinoderms and cnidarians are more closely related than enchinoderms and mammals

Because they are triploblastic ( Triblastica ).

Explanation:

Their body is composed of endoderm, mesoderm and ectoderm. While Cnidaria are Diblastica, so they are composed only from two layers: endoderm and ectoderm.

In addition larvae of Echinoderms are bilaterally symmetrical and they become nearly-radial only as adults.

i'm thinking (a) to keep sand in place; ////////////

explanation: a sand fence or sandbreak, like a snow fence, is used to force windblown, drifting sand to accumulate in a desired place. sand fences are employed to control erosion, sand dune stabilization, keep sand off roadways, and to recruit new material in desert areas.

thrombocytopenia, which is a deficiency in blood platelets, can cause bleeding and bruising in the dermis similar to senile purpura. other possible causes include: exposure to ultraviolet rays and aging skin are common causes of senile purpura. senile purpura may also be a sign of collagen loss in the skin and bones.