English (Source)
Towers gain <Highlight>1</> level immediately when placed on the most recently explored tile, but towers always have to participate in one wave before being able to be sold.
Chinese Translation
当防御塔被放置在最近探索的地块上时会立刻获得 <Highlight>1</> 级，但防御塔必须先参与一波战斗后才能被出售。