Which of the following is an example of a conditioned reinforcer?

A conditioned reinforcer is a stimulus that acquires its reinforcing value through its association with a primary reinforcer. In this case, toys serve as an example of a conditioned reinforcer. They often become reinforcing through their connection to other reinforcing experiences, such as play or enjoyment, which can be tied back to primary reinforcers like food or social interaction.

The other options represent primary reinforcers, which are naturally reinforcing without any prior learning or association. Food, water, and sleep are biological needs essential for survival and do not require any conditioning to be considered reinforcing. In contrast, toys need to be associated with enjoyable experiences or outcomes to gain their reinforcing properties, making them a clear example of a conditioned reinforcer.