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>