there was a book and two pens lying on the table

在there be句型中谓语动词遵循“就近原则”，就是与最近的名词保持一致，这句中 a book 比two pens 更靠近be动词，所以用was而不用were

There be句型中谓语动词遵循“就近原则”
be动词的形式根据后面的名词的单复数而定，即
There was a book and two pens lying on the table.
There were two pens and a book lying on the table.

因为AND前面是A BOOK.

就近原则哈。