pick up在这里是什么意思？

绿箭王子

--------------------------------------------------------------------------------
  the group wintered near the Mandan villages in the center of what is now North Dakota. Resuming their journey in the spring of 1805. the men worked their way along the Missouri to its source and then crossed the mountains of western Montana and Idabo. ～～～～～Picking up～～～～ a tributary of the Columbia River , they continued westward until they reached the Pacific Ocean, where they stayed until the following spring.
谢谢～～怎么想也想不出来～～～
95nian 10 yue 4 pian  

necrophile

following 接着，有些地方翻成“找到”。 但是“接着”更合题

chipmunk

I just checked dictionary, pick up means: acceleration or improvement.

necrophile

查了文曲星，我想光查PICK UP对于这道题不够，"pick up the threads" 结构跟原文差不多，意思是：“重新捡起来做，接着做，继续做。” 从此，乱七八糟，西了虎度，的推出“PICKING UP” 是“FOLLOWING”的意思。

有点胡扯，强词夺理，不过我做时选的就是“FOLLOWING”。