Which of the following transmission lines will give the best match to the base of a quarter-wave ground-plane antenna?

A standard quarter-wave ground-plane antenna is an unbalanced antenna that presents a feedpoint impedance typically between 36 and 50 ohms, depending on the angle of its radials. This makes a 50-ohm coaxial cable the best choice for a direct, efficient match. Using 75-ohm coaxial cable would result in a higher mismatch. Balanced transmission lines, such as 300-ohm twin-lead, are completely inappropriate here; not only is 300 ohms a massive impedance mismatch for a 36-50 ohm feedpoint, but connecting a balanced line to an unbalanced antenna without a balun causes severe common-mode currents and radiation from the feedline.