Although Tom is not that smart,he is as ( ) as his classmate

Although Tom is not that smart,he is as ( ) as his classmates.
选项:
a、a diligent student
b、diligent a student
c、a student diligent
d、student a diligent

　　答案是b
　　这里考察as + 名词+ as句式
　　名词分三种情况,可数名词单数 as + 形容词 + a + 可数名词单数+ as
　　eg ,He is as good a student as she .
　　可数名词复数,as + many +可数名词复数＋　as
　　eg．　This　factory　produce　as　many　cars　as　that　one．
　　不可数名词,　as＋much　＋　不可数名词　＋　as
　　He　earns　as　much　money　as　she　．