Which of the following is an assumption implicit in process$-$costing?

Question $4$ options:

a$)$

All completed units receive the same amount of direct material inputs and the same amount of conversion costs

b$)$

All completed units receive more direct material inputs than units in process

c$)$

All completed units receive less direct material inputs than units in process

d$)$

Ending inventory is always zero for the cost calculations