Which of the following situations involves an external attribution? A. Desiree believes she did well on the exam because she is intelligent.
B. Thomas believes he did well on the exam because he knows a lot about math.
C. Nick believes he did well on the exam because the exam was easy.
D. Cassidy believes she did well on the exam because she tried very hard.

 C. Nick believes he did well on the exam because the exam was easy.

Explanation:

Nick is relating his performance on the exam to an external factor (the difficulty of the exam being easy).

All the other answers are relating the exam to internal factors such as intelligence, personal knowledge, and effort.

the right option is; decreased genetic variation  

decreased genetic variation describes the effect of this environmental change.

genetic variation is the naturally occurring genetic diversities or differences between organisms of the same species in a population. genetic variation allows the survival and adaptability of a species when they encounter changing environmental conditions. when an endangered species reduces, it loses genetic variation which may not be restored even if the species rebound and will only be recovered through the gradual collection of mutations over many years.