B – vary. The word ‘vary’ here means that each specie can be different from one another. ‘Change’ would mean changing over time, rather than having variety between different animals. ‘Shift’ is about moving from one state to another. ‘Alter’ is normally used with an object – ‘to alter something’.
D – feared. ‘Scared’ and ‘frightened’ can’t be used because that would mean that wolves are scared of these people and animals. It is the opposite – both humans and animals are afraid of them. This can be inferred from the fact that ‘small animals’ and ‘people’ are put in the same group and it is clear that wolves can’t afraid of smaller species. ‘Afraid’ can’t be used as it doesn’t work with preposition ‘by’
D – social. ‘Social animal’ is a common collocation.
A – partner. The idea of monogamy is about having one mating partner, as opposed to polygamy. Other words in the list do not have the meaning of mating.
A – prey. This is the only verb that works with the ‘on’ preposition. Other verbs take no preposition.
B – control. Another common collocation – ‘to go/get out of control’. ‘To get out of shape’ has the meaning ‘to lose shape or form’.
B – upsetting. ‘To upset balance’ means to make one of the sides of the system more powerful or prevalent. ‘Destroy’ shouldn’t be used here as it has a different, more dramatic meaning of ruining the system completely, which is not the case.
D – success. ‘Without (much/any) success’ is a strong collocation.