Please help me with the right option

Ali is a member of a family that consists of him, his father, his mother and his older brother. Each member of the family has his own mobile phone. Each mobile phone is on a post-paid plan, for which a monthly bill is received at the end of each month. The electricity, on the other hand, is provided to the entire house in general, with one bill is received at the end of each month. The father has recently received the phone bill of Ali and wishes to do some analysis of the phone consumption. Assuming that the value of the phone bill is calculated based on the number of minutes consumed plus a constant monthly subscription fee. In the above information, the cost of the phone bill to Ali is: O a. An indirect mixed cost O b. A direct, variable cost O c. An indirect fixed cost O d. An indirect, variable cost O e. A direct mixed cost