The sourcing strategies including; maintaining safety and/or strategic stocks, developing contingency plans, strengthening relationships, and searching for alternatives, are appropriate for which item category? non-critical items bottleneck items leverage items strategic items

All of these fall under the Bottleneck items of strategic sourcing. 
Bottleneck explains situations when there is a high amount of risk and the availability of the item is low. There are not a lot of supplies to pick from but the item is in demand, this leads to procurement problems. Companies use strategic sourcing to try and red the cost of an item while keeping or improving the quality of it.