An object 4 cm in size, is placed at 20 cm in front of a concave mirror of focal length 10 cm. At what distance from the mirror should a screen be placed in order to obtain a sharp image?

• A. 20 cm from the mirror
• B. 10 cm from the mirror
• C. \(\dfrac{20}{3}\) cm from the mirror
• D. \(\dfrac{10}{3}\) cm from the mirror