In paracrine signaling, the signaling molecule: acts on the same cells that secreted the signaling molecule. is always integrated into the plasma membrane of the signaling cell. is carried to the target cells by the blood. acts on cells in close proximity to the secreting cell. acts on target cells far away from the secreting cell.

Acts on cells in close proximity to the secreting cell.

Explanation:

In paracrine signaling, the molecules secreted by a cell show their impact on the cells which are nearby or in very close proximity.

For example:

Nerve impulse transmission from presynaptic neuron to postsynaptic neuron. When ever a stimulus is detected by our body, transmission of nerve impulse occurs so that our body could respond  to that stimulus accordingly. During transmission, the presynaptic neuron releases signaling molecules known as neurotransmitters in the synaptic cleft which is present in between presynaptic neuron and postsynaptic neurons. From synaptic cleft, these neurotransmitters reach the receptors present on the neighboring postsynaptic neurons which finally transmit the message to the muscles to generate a response to the stimuli.

any abiotic or biotic factor in an ecosystem that causes a population's size to slow or decrease is a limiting factor.