Coordination and response — practice question

The events taking place at a synapse are shown below. They are not arranged in the right order. What is the correct sequence of events?

• A2 → 4 → 1 → 3
• B2 → 4 → 3 → 1
• C4 → 2 → 1 → 3
• D4 → 2 → 3 → 1