Self-fertilization is avoided in sponges because
a. there is no way for sperm to enter the sponge.
b. the sperm do not possess the enzyme needed to penetrate the egg.
c. sperm and eggs are not produced at the same time.
d. none of the above is true; self-fertilization is common in sponges.

Compare and contrast region e in the illustration above with region d. describe the physical characteristics of each region.

How many years would it take the atlantic ocean to grow 500 centimeters? show your work.

Some birds look for food near cattle and other livestock. the movement of the cattle churns up the ground, making insects available to the birds. the cattle appear to be unaffected by the presence of the birds. what kind of relationship exists between the birds and the cattle? o a. parasitism o b. commensalism o c. predation o d. mutualism