tree search for an immobile hider

例句：

1. 1. The tree is tall andhas a strong trunk.
   这棵树很高，树干很粗壮。
2. 2. Trees are an importantpart of our ecosystem.
   树木是我们生态系统的重要组成部分。
3. 3.The forest was filled with the sound ofbirds singing.
   森林里充满了鸟儿的歌唱声。