Which of the following is a variable cost? O a) A cost that is $25,900 when production is 35,000, and $25,900 when production is 37,500. ( b) A cost that is $12,950 when production is 35,000, and $13,875 when production is 37,500. O c) A cost that is $12,950 when production is 35,000, and $12,950 when production is 37,500. O d) A cost that is $12,950 when production is 35,000, and $25,900 when production is 37,500