Positive feedback in a system is

words of praise
a benefit for the entire system
an interaction that benefits one element
an event that benefits one part while weakening another

Positive feedback in a system is a benefit for the entire system

Option B

Explanation:

The positive mechanism is a stimuli that the body exhibits when in time of need which actually benefits the entire system. When required the positive feedback runs to rescue and neutralize the effect caused by the negative impact which paves a way to maintain equilibrium throughout the body.

Many examples can be cited for this like blood clotting, during labor and even in ripening of fruits. Positive and negative feedback work hand in hand to maintain homeostasis in place. Positive feedback is required to enhance the system while the negative feedback is to inhibit the activity.

B. Neurotransmitters send signals from neuron to neuron.

Explanation:

Lack of neurotransmitters may cause problems because neurotransmitters send signals from neuron to neuron.