单选题 Twitter, the micro-blogging service used by tens of millions of people, went off-line last month. It blamed the trouble on a malicious programmer in Russia who was trying to shut down the account of a user in neighboring Georgi

• a. It is astonishing the local actions of a small number of programmers can bring an entire Internet service to its knees, but that appears to have been the case.
  What seems to be a big problem for Internet services?A. A few programmers can break down an entire Internet service.B. There are too many malicious programmers attacking the Internet.C. There are so many users that the Internet cannot burden the load.D. The competition is so fierce that many websites have gone bankrupt.