Gause's law is true only when

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: Abingdon tortoise in Galapagos islands became extinct within a decade after goats were introduced.
Reason $R$: Goats were more efficient at browsing than Abingdon tortoise.
In the light of the above statements, choose the most appropriate answer from the options given below:

Which of the following exhibits parasitism on the stem of a plant?

From the given options,identify the correct combination of population interactions that correspond to the symbols given here.

The interaction between "Cuckoo and Crow" is an example of:

Which of the following is an example of a parasite living on another parasite?