问题：FACTORS=[["x",5],["z",3]]，执行结果为 xz，但是 FACTORS=[[“c”,9],["x",5],["z",3]] 执行结果为 c，我预计的结果应该是 cxz，求问原因。 代码如下：

class Roman
  def initialize(value)
  @value = value
end

FACTORS=[["x",5],["z",3]]  #返回xz
#FACTORS=[[“c”,9],["x",5],["z",3]  #返回c

  def to_s
    value = @value
    roman = ""
    for code, factor in FACTORS
    count, value = value.divmod(factor)
      if !count.zero?
        roman << code
      end
    end
    roman
  end
end

a = Roman.new(9).to_s
puts a