Which of the following interactions results in a negative effect (harm) for both interacting species?

High density of an elephant population in a given area results in:

Two butterfly species are competing for the same nectar of a flower in a garden. To survive and coexist together,they may avoid competition in the same garden by:

Choose the correct statements regarding population interactions between two species.
$A$. In both parasitism and commensalism, only one species benefits and the other species is harmed.
$B$. Both species benefit in mutualism.
$C$. Both species benefit in commensalism.
$D$. In parasitism, only one species benefits and the other species is harmed.
$E$. In amensalism, one species is harmed and the other is unaffected.

What does Gause's Competitive Exclusion Principle state?

Choose the correct group for commensalism from the following:
$(a)$ The cattle egret and grazing cattle
$(b)$ Barnacle balanus and Barnacle chathamalus
$(c)$ Goat and Abingdon turtle from Galapagos island
$(d)$ Barnacles growing on the back of whale