"Collects stones" 的第三人称单数形式是 "collects stones".
"Collects" 是 "collect" 的第三人称单数形式。"Collect" 是英语单词，意思是 "收集"。
例句：
He collects stones as a hobby. (他喜欢收集石头。)
She collects stones from different parts of the world. (她从世界各地收集石头。)
They collect stones to decorate their garden. (他们收集石头来装饰花园。)