Atlantic puffins are ______; each pair of parents stays together for years and shares duties involving the incubation of eggs and the feeding of chicks.

A、 monogamous
B、 gregarious
C、 aggressive
D、 heterogeneous
E、 indistinguishable

【正确答案】 A

【答案解析】The answer is defined by the phrase that follows: "Each pair of parents stays together for years."