Each book____broken down into several units.在空白处应该填is,was,has还是have?为什么?

Each book____broken down into several units.在空白处应该填is,was,has还是have?为什么? each each each each each For each for each love each meet each think each at each .on each.each.in each的用法 greeting each each用法 each picture. each of in each each是什么意思