It took several hundred years paper-making spread to western countries.A. whenB. beforeC.

问题补充：

It took several hundred years paper-making spread to western countries.

A. when

B. before

C. after

D. since

答案：

A. when

(答案→)B. before

C. after

D. since

解析：连词辨析。 A．当……时 B．在……之前 C．在……之后 D自从……。

句意：造纸术花了几百年才传到西方国家。意思是在造纸术完全传到西方之前用了几百年的时间，故选B。