Why restrict the table to only two keywords per book?

为什么要将这个表限制为每本书只有两个关键字？

youdao

The new price of $9.99 per book in the Sony eBook store is quite interesting.

索尼电子书店9.99美元的新价格确实引人注目。

youdao

If the book price happens to be an attribute, then it can occur at most once per book element.

如果book price是属性，则该属性在每个book元素至多出现一次。

youdao

While publishers ended up earning less per book because of the revenue share to e-reader companies, they regained control over their property.

WSJ: Crovitz: Steve Jobs, Price Fixer?

One example of a company that actually did make large repurchases of shares substantially below book value in 2011 is American Capital ( NASDAQ: ACAS), which announced it bought back millions of shares of its own stock, at prices considerably below its most recent reported book value per share, thereby elevating the per-share book value of the remaining shares.

FORBES: The Importance of Book Value

With this method, we gain total control of the product, and we make double, triple or even quadruple the amount of money per each book sold.

FORBES: Age of Context Takes A Sponsorship Route