Option 1: Reduces substantially - This option implies that the current in the circuit decreases significantly when a short-circuit occurs. However, this is not accurate. When a short-circuit occurs, it creates a low-resistance path for the current to bypass the intended circuit. As a result, the current increases rather than decreases.

Option 2: Does not change - This option suggests that the current remains the same when a short-circuit occurs. However, this is also incorrect. A short-circuit provides a direct path with a significantly lower resistance, leading to a surge in current flow.

Option 3: Increases heavily - This is the correct answer. When a short-circuit occurs, the resistance in the circuit decreases dramatically, allowing a higher amount of current to flow through the circuit. The increase in current can be substantial and can potentially lead to damaging consequences such as overheating, electrical fires, and damage to the components.

Option 4: Varies continuously - This option suggests that the current in the circuit fluctuates continuously when a short-circuit occurs. However, this is not the case. Once a short-circuit is established, the current will increase and remain at a high level until the short-circuit is resolved.

In summary, during a short-c