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.
  Who was responsible for the collapse of Twitter?A. All its users.B. A malicious programmer in Russia.C. A small number of programmers.D. A user in neighboring Georgia,