The AT&T Long-Distance Network Did Not Collapse Entirely on January

The AT&T long-distance network did not collapse entirely on January 15, 1990, because

A) the U.S. Secret Service arrested the culprits before they could do any further damage.
B) AT&T technicians rapidly fixed the software bug in the routing switches.
C) MCI loaned some equipment to AT&T.
D) the faulty computers shut themselves off before they could do any further damage.
E) not all the routing switches had been converted to the latest software.