In order that current should flow without causing excessive heating or voltage drop, the relay contacts should

The correct answer is D.

The relay contacts should have low contact resistance, be clean and smooth, and be of sufficient size and proper shape.

• Low contact resistance ensures that the current flows smoothly and without causing excessive heating.
• Clean and smooth contacts ensure that there is good electrical contact between the two surfaces, which also helps to reduce heating.
• Sufficient size and proper shape ensure that the contacts can handle the current that is flowing through them.

If any of these conditions are not met, it can lead to excessive heating or voltage drop, which can damage the relay or the equipment that it is controlling.