Consider the following statements about absorption costing $($GAAP$)$ and variable costing $($decision making$)$:

I. Variable costing is consistent with contribution reporting and cost$-$volume$-$profit $($CVP$)$ analysis

II$.$ Absorption costing must be used for external financial reporting

III. A number of companies use both absorption costing and variable costing

Which of the above statements is $($are$)$ true?