Which agricultural practice focuses on selective breeding?

Selective breeding is a process where specific plants or animals with desirable traits are chosen to reproduce, aiming to enhance those traits in future generations. This practice is at the core of purebred operation, where breeding is conducted to maintain or improve specific qualities, such as disease resistance, growth rate, or physical appearance.

In contrast, organic farming emphasizes natural growth practices without synthetic inputs and does not inherently focus on selective breeding as its primary tenet. Genetic engineering involves altering an organism's DNA directly, which is different from the traditional method of selective breeding that relies on natural reproduction processes. Hydroponics pertains to growing plants in a nutrient-rich solution without soil and does not inherently involve selective breeding practices.

Thus, the focus on selective breeding within purebred operations makes this the most accurate choice among the options provided.