同学你好，该知识点来自沪江网校《英语零基础直达大学六级【开学季特惠班】》的课程，想要更系统的学习，欢迎进入课程学习。不仅可以和更多的同学一起学习，而且还有老师、助教随时的学习指导和知识点解答哦。

同学你好~
这句话相当于The writer saw what against the wall.
against the wall是介词短语，against不可以去掉，意思是“紧靠；倚；碰；撞”
Put the piano there, against the wall.
把钢琴放在那儿，紧靠着墙。

Lined up against the wall, there were long thin wires attached to metal spheres.  靠墙排列着许多细长的电线，而电线又连着金属球。

祝同学学习进步~