Direct costs and decision making.

Thanks for your reply. Now see this question,
Which of the following statements is not true? 
(a) Fixed costs are fixed over a range of activity (b) Variable costs are fixed per unit of production (c) Fixed cost per unit is variable with a change in the production level 
(d) Direct costs are always relevant for decision
 making .

Correct option given is(d). It says direct costs are not relevant. How??