Holding extra stocks will always improve customer service levels, or at least reduce the risk of them falling.
This implies that if an organisation aims at higher service levels, they should have larger safety stock.
However, increasing safety stock is not the only solution to improve service level. The widespread adoption of just-in-time (JIT) techniques particularly in the automotive industry has greatly reduced costs with increased service levels as well as the additional benefit of increased problem visibility.
The correct answer should be 'A safety stock is not always required to achieve a required service level'.