六年级英语下册第四单元的句子主要包括以下内容：

一、重点句型

描述变化

- "I have changed a lot. Before, I was short and thin. But now, I'm tall and strong..."（我变化很大。过去又矮又瘦，现在又高又壮...）

- "Mike: Right. Before, I was quiet. Now, I'm very active in class..."（迈克：没错。以前我很安静，现在上课很活跃...）

假期经历

- "Where did you go on your holiday？ I went to Xinjiang. How did you go there？ I went by train."（你去哪里度假了？我去新疆。你怎么去的？我坐火车去的。）

二、其他常见句型

现在与过去对比

"He used to be quiet and shy. However, he has become more outgoing..."（他过去很文静害羞，现在变得外向了...）

日常场景

"There are some students in the classroom. My father gets up very early..."（教室里有一些学生。我爸爸起得很早...）

三、注意事项

该单元侧重现在完成时态（如"have changed"）和一般过去时态（如"used to be"）的用法；

部分句子需注意主谓一致（如单复数形式）。