Polarity reversal enables forward bias in the diode lamp.

Steps:

• Identify the lamp as a diode (e.g., LED), which conducts only in one direction.
• Check battery connections: reversed polarity applies reverse bias, blocking current.
• Reverse battery terminals to apply forward bias, allowing current flow.
• Verify lamp lights when voltage exceeds threshold in correct direction.

Why C is correct:

• Diodes conduct under forward bias (anode positive relative to cathode); reversing battery connections aligns polarity per diode law, enabling current.

Why the others are wrong:

• A: Voltage change doesn't fix reverse bias blocking current.
• B: Fuse insertion protects circuits but doesn't correct polarity issue.
• D: Lamp connections are symmetric for diodes; reversal won't change bias direction.

Final answer: C