D. the knowledge point examined in this question is the difference between complex reflection and simple reflection. Does the essential difference between simple reflex and complex reflex involve the cerebral cortex? Without the cerebral cortex, the reflection of the nerve center below the cerebral cortex is a simple reflection, and the reflection of the reflected nerve center on the cerebral cortex is a complex reflection. When others eat meat, they also secrete saliva. This reflex phenomenon is only after birth. It is a kind of acquired complex reflex, which is based on unconditional reflex and completed with the participation of cerebral cortex through a certain process. This is an advanced nerve reflex activity, which can fade or weaken.