阅读理解（只个一个问题）The Internet is a big place.Nobody has the time

阅读理解（只个一个问题）
The Internet is a big place.Nobody has the time to look at every webpage to find something.Searching engines like Yahoo gives us the help we need.
Yahoo started in 1994 as the project of two Stanford University students,David Filo and Jerry Yang.They,making,their,favourite,some,by,webpages,started,of.As the number of webpages became larger,they made a database to keep their information.They let everybody use it for free.Soon,thousands of people were using their service.
They then made a new kind of software.It looked at webpages all over the Internet.It could then take that information and arrange it for someone to look at.If you search for,say,“blue whales,” the engine will give you a list of webpages with those words.
Yahoo became a public company in 1996.Filo and Yang,still young men,became rich.As their company grew,they continued to work hard.They improved their software.They also added more services,like shopping,free e-mail,and an auction service.And,they started Yahoo sites in many different countries and languages.
Yahoo.com is famous on the Internet.And unlike most other Web companies,Yahoo actually earns money.
After Filo and Yang became rich,they _________
A became lazy B didn't work hard C stoopped working at Yahoo D kept working hard
我认为是D,但书上的标准答案是A