points are not selected when making a spring mechanism

Hi, I was trying to make a simple spring mechanism for school project

When creating this, I faced a problem that two pairs of dots are not simultaneously selected.

As shown in the attached figure, pnt0 and pnt1 were set on the top and bottom of each part, respectively.
I tried to select the other point by pressing and hold Ctrl key , but it didn't even work.
How should I solve this problem? I don't know what the problem is.