Which of the following statements regarding the "theory of constraints" $($TOC$)$ is TRUE?

In order to maximize throughput, all parts of the operation needs to be operating close to full capacity.

Increasing the capacity of the bottleneck is expensive, and thus should be avoided at all costs.

One place where inventories should be built up is in front of the bottleneck operation.

A bottleneck operation should occasionally have a down time to ensure smooth operation.