Which of the following best explains a method by which plants use long-distance signaling to carry out cell communication?

1. Gas hormones are released and travel through the air to reach their target cells.
2. Growth factors are released into extracellular fluid toward target cells via
paracrine signaling.
3. Molecules travel down a concentration gradient to target cells through
plasmodesmata.
4. Neurotransmitters carry chemical signals from dendrites to axons across
synapses.