The New York Stock Exchange Has a Feature Called a "Circuit

The New York Stock Exchange has a feature called a "circuit breaker" which

A) "turns out the lights" if the Dow-Jones average falls over 100 points in one hour.
B) stops trading in equities for one hour should the DJIA fall more than 250 points.
C) stops trading in equities for one day if the DJIA falls more than 250 points.
D) has proved quite effective in stopping the market from falling precipitously.