premise: U.S. stocks opened higher on Tuesday as investors were waiting for election results.
  In the opening trading, the Dow Jones Industrial Average rose 1.84 to 12,107.39. The Standard & Poor's 500 index rose 0.08 to 1,379.86, and the Nasdaq composite index climbed 0.64 to 2,366.59.
  Crude oil prices rose slightly in electronic trade Tuesday amid supply concern of Nigeria.
  Output of 55,000 barrels per day of oil was cut in Nigeria when armed protesters forced the closure of a flow stationbelonging to the Italian oil company Agip in the the oil-rich Niger Delta.
   Why was output of oil cut in Nigeria?
hypothesis: armed protesters forced the closure of a flow station