Which of the following is NOT a true statement about cost behavior patterns $($within the relevant range$)?$

Fixed costs in total remain unchanged for a given time period, despite changes in the related level of total activity or volume of output produced.

The cost behavior of variable costs in total is sometimes described as strictly variable or proportionately variable.

A variable cost decreases on a per$-$unit basis as the number of production units increases.

A variable cost changes in total in proportion to changes in the related level of total activity or volume of output produced.

IDON'T KNOW YET