在英语表达中，“that is to say”是一个非常实用且优雅的短语，通常用于补充说明或进一步解释前面提到的内容。它既可以作为连接词使用，也可以单独成句，帮助我们更清晰地传达信息。下面通过几个具体例子，展示如何灵活运用这一短语。

示例一：

原句：She has been working hard these days.

扩展句：She has been working hard these days, that is to say, she is trying her best to finish the project on time.

分析：这里“that is to say”起到了承上启下的作用，将前一句的工作努力与后文的具体目标联系起来，使表达更加连贯和具体。

示例二：

原句：He is not very good at sports.

扩展句：He is not very good at sports, that is to say, he finds it difficult to keep up with his teammates during training sessions.

分析：通过添加“that is to say”，不仅解释了他不擅长运动的原因，还进一步描述了具体场景，让读者能够更好地理解情况。

示例三：

原句：The weather was bad yesterday.

扩展句：The weather was bad yesterday, that is to say, it rained heavily all day long without stopping.

分析：“that is to say”在这里将天气状况进行了具体化，避免了模糊不清的表述，使描述更具象化。

小结：

无论是书面写作还是日常对话，“that is to say”都能很好地帮助我们补充细节或深化含义。掌握好这个短语的应用技巧，可以让语言表达更加丰富多样。希望以上例子能给大家带来启发，在实际交流中尝试使用这一工具吧！