In ideal projectile motion on level ground (ignore air resistance), a firearm fires a projectile with fixed speed $v$ from ground level. Which statement about the projectile’s maximum horizontal range is true?

• A. The maximum range occurs when the launch angle is $30°$.
• B. The range is the same for all launch angles because gravity acts only vertically.
• C. The maximum range occurs for a horizontal launch, $0°$.
• D. The maximum range occurs when the launch angle is $45°$.

Answer: (D)