Firms' costs, revenue and objectives — practice question

The diagram illustrates a firm’s average total costs (ATC) and average fixed costs (AFC). Which statement is correct?

• AAt output $X$, average variable costs are lower than average fixed costs.
• BAt output $Y$, total variable costs are greater than total fixed costs.
• CBetween outputs $W$ and $Z$, total fixed costs are falling.
• DBetween outputs $W$ and $Y$, average variable costs have not changed.