语法高手看过来The number of magazines issued this year has increase

语法高手看过来
The number of magazines issued this year has increased to ( )of last year.
A twice as many as those
Btwice as much as those
Ctwice as many as that
D as many as that
答案是B解释是本题主语是the number,故用much修饰,those 指magazines,所以选B.我想问的是2个as是什么词性,是副词还是什么的?