可以是副词,也可以是介词。介词用法比较少见,但是韦氏词典上有介词这一项,如图:
![](https://video.ask-data.xyz/img.php?b=https://iknow-pic.cdn.bcebos.com/d1a20cf431adcbef328768b5a0af2edda2cc9fd5?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto)
又如下一例句,是托福TPO听力中的原句:We now know that there was still a widespread trading network up and down a long portion of the coast of what is modern-day Mexico and Central America for more than two centuries after the golden era ended.