16.This is a purely _______ problem, not a political one.
A. additional B. assiduous C. adamant D. academic

<academic>
academic adj.学术的、理论的
</academic>

<additional>
additional 额外的、附加的
additive 添加剂
addendum 补充、附录
adder 蝰蛇
deaf as an adder 充耳不闻
</additional>

<assiduous>
assiduous 勤奋的、好学的
insidious 阴险的、狡诈的
preside (over) 主持
consider 考虑
</assiduous>

<adamant>
adamant 固执的
</adamant>