Which of the following is a complex sentence?（）
You throw a stone at the window.
You throw a stone at the window and I'll scream.
If you throw a stone at the window, I'll scream.
The baby is crying.
A选项是简单句，B选项是并列句，C选项是条件状语从句，属于复杂句。D选项是简单句。因此选择C选项。
