Female capuchin monkeys were chosen for the research most probably because they are __

Female capuchin monkeys were chosen for the research most probably because they are ________.

[A] more inclined to weigh what they get

[B] attentive to researchers’ instructions

[C] nice in both appearance and temperament

[D] more generous than their male companions

请帮忙给出正确答案和分析，谢谢！