Study the following statements.

a) In general herbivores and plants appear to be more adversely affected by competition than carnivores.

b) Biological control methods adopted in agricultural pest control are based on the ability of the predator to regulate prey population.

c) In endoparasites morphological and anatomical features are complicated and reproductive potentials are simplified. 

d) Evolutionary changes through natural selection take place at organism level but not at population level.

How many of the above are correct?