polycyclic compound

例句：

1. 1.The molecule is composed of several polycyclic rings.
   这个分子由几个多环环组成。
2. 2.Polycyclic compounds are common in the natural world.
   多环化合物在自然界中很常见。
3. 3. Polycyclic compounds have been used as building blocks for many synthetic materials.
   多环化合物被用作合成材料的构建块。