____ the students came into the classroom, they began to study attentively. [ ]

A. Hardly

B. The moment

C. Unless

D. At the moment

六年级一班学生参加植树活动，平均每人分到12棵小树苗．若只发给女生，平均每人可分得20棵：若只发给男生，平均每人可分得______棵．