（2015•南宁）尿素[CO（NH2）2]是一种常用的化学肥料，它属于（ ）
A：钾肥
B：磷肥
C：氮肥
D：复合肥
下列石油运输路线，错误的是（ ）
Susan is a top student in our class, so she never _______ an exam.
He is a kind doctor, and these years letters of thanks have been f____ in.
