The basic difference between periodic systems $($P$-$model$)$ and fixed$-$order quantity systems $($Q$-$model$)$ is:

Question $4$ options:

Q$-$models are event triggered while P models are time triggered

Q$-$models are time triggered while P models are event triggered

P$-$models favor more expensive items

P$-$models are more appropriate for important items such as critical repair parts

None of the above