电子教科书的英文：
e-textbook

a graduated series of textbooks
分等级的教科书系列

A part of the textbooks have arrived.
一小部分教科书已经运到了。

Lectures work in tandem with the textbook.
授课与教科书的作用互相串联。

This textbook consists of 18 chapters.
这本教材包含18章。

Our textbook has many figures to help explain the lessons.
我们的教科书有许多图表帮助解释课文。