Which of the following is TRUE (only one correct answer): O Variable costs are defined as those costs which vary proportionally inverse to volume of activity O Fixed costs are those costs not subjected to variations along the time O Fixed cost remains constant at the unitary base OTotal variable costs are those costs not subjected to variations along the time O Variable cost remains constant at the unitary base O Discretional costs are defined as fixed costs not included into the relevance range O Budgeted costs are defined as variable costs linked to the manufacturing activity O No one of the above