Cells are classified by their shapes and sizes and by the relative complexity of their biochemical processes, as well as their genetic content.
在以下文本开头插入一个语义适当的句子，使得话题能够平稳引入。
所有的生物都是由细胞组成的，这些细胞是微观的，通常只能在显微镜下看到。Cells are classified by their shapes and sizes and by the relative complexity of their biochemical processes, as well as their genetic content.