简单句与复杂句的区别

章振邦先生在新编英语语法课程的简单句与复杂句中讲到：

假如构成分句成分的词组本身带有从属分句，那样这个句子仍然是简单句。比如：

The studentsI teach have made better grades in the past few weeks.请问这个词组本身带有些从属分句是红字部分吗？为何词组带有从属分句就是简单句

但若某个句子成分直接由从属分句表示，那样这种句子便不是简单句而是复杂句。例：

The students would have made better grades if they had studied hard.

The boy can stay in the room so long as he keeps quiet.

What he said is not true. I didnt understand what he meant. 请问老师直接由从属分句表示的意思是？这四个句子与第一个的不同之处？还请老师明晰解说简单句与复杂句有什么区别。感谢！

你让老师退还鲜花，没人敢解答你的问题了。