need help

Given the following costs for Bently Company, classify each cost as either variable, fixed, or mixed.

                                                                        Total Cost at

                                                         2,000 Units                  3,000 Units

                              Cost A                  $12,900                       $19,350

                              Cost B                    12,300                         16,650

                              Cost C                    13,000                         13,000 

                  a.   Cost A and Cost B are variable; Cost C is fixed.

                  b.   Cost A is variable; Cost B is mixed; Cost C is fixed.

                  c.   Cost A and Cost B are mixed; Cost C is fixed.

                  d.   Cost A is mixed; Cost B is variable; Cost C is fixed.