The correct answer is A: Very high impedance. A 1/4-wavelength transmission line shorted at the far end presents very high impedance to an RF generator. A quarter-wavelength line transforms a short (0 ohms) to an open (very high impedance) at the input. Transmission lines transform impedances based on length. A shorted 1/4-wavelength line inverts the impedance - a short at the far end becomes an open (very high impedance) at the input. This is the opposite of an open 1/4-wavelength line, which transforms an open to a short. This property is useful for creating high-impedance points, blocking DC, or creating RF chokes. The 1/4-wavelength transformation is fundamental to many matching and filtering applications.