Concept:A strong argument must be relevant, logical, and important for the given statement.
Explanation:Argument I says street lights should not be switched off because crime and accidents increase without them.
This is a strong safety reason and directly opposes switching off.
Argument II says street lights should be switched off because few vehicles use roads after midnight and electricity is expensive.
This is a strong economic reason and directly supports switching off.
Both arguments are based on valid concerns, so both are strong.
Answer:Both arguments I and II are strong, so option C is correct.