That's a wire running down the middle, and not only is it a wire, if you take that piano circuit, you can thumbtack into the middle of a pencil, and you can lay out wire on the page, too, and get electrical current to run through it.
有一根电线从中贯穿 这根电线可不简单 如果把钢琴电路板 钉上铅笔笔身 就可在纸上规划电路 让电流通过。