input: Write a python function to calculate mean, variance, median, and mode using the Statistics class.
  ```python
  stats = Statistics()
  stats.add_score(1)
  stats.add_score(2)
  stats.add_score(2)
  stats.add_score(3)
  stats.add_score(4)
  assert stats.mean() == 2.4
  assert stats.variance() == 1.04
  assert stats.median() == 2
  assert stats.mode() == [2]
  
  stats2 = Statistics()
  stats2.add_score(10)
  stats2.add_score(20)
  stats2.add_score(30)
  assert stats2.mean() == 20
  assert stats2.variance() == 66.66666666666667
  assert stats2.median() == 20
  assert stats2.mode() == [10, 20, 30]
output: from statistics import mean, variance, median, mode, multimode
  
  class Statistics:
      def __init__(self):
          self.scores = []
  
      def add_score(self, score):
          self.scores.append(score)
  
      def mean(self):
          return mean(self.scores)
  
      def variance(self):
          return variance(self.scores)
  
      def median(self):
          return median(self.scores)
  
      def mode(self):
          return multimode(self.scores)