Explanation: A significant loss in VHF receiver sensitivity can be caused by a condition that prevents the internal circuitry from functioning optimally. * **A) A reading of 9.6 when a voltmeter is connected between the positive side of the radio’s DC line and ground.** Most amateur radio transceivers are designed to operate from a nominal 12-13.8 Volt DC supply. A voltage reading of 9.6V is significantly lower than the intended operating voltage. Undervoltage can starve the radio's internal circuits, such as RF amplifiers, mixers, and IF stages, leading to reduced gain, improper biasing, and overall poor performance, which manifests as a significant loss in receiver sensitivity (its ability to pick up weak signals). * **B) The presence of a -90dbm signal measured at the 2nd IF output with the receiver tuned to the desired input.** A -90 dBm signal at the Intermediate Frequency (IF) output is a relatively weak signal. If the receiver is tuned to a very weak input signal, observing -90 dBm at the IF output might be perfectly normal operation for a receiver with good sensitivity. This value does not inherently indicate a *loss* of sensitivity; it could just mean the receiver is working to amplify a very weak input. * **C) An internal signal that is very weak in comparison to the desired signal at the output of the second IF stage.** This statement is ambiguous. If it refers to an *undesired* internal signal (like noise or spurious emissions) that is very weak compared to the desired signal, this would be an ideal scenario, as it means the desired signal is well above internal interference, suggesting *good* rather than poor sensitivity. It does not describe a condition causing a loss of sensitivity. * **D) Replacing (75 ohm) RG-59/U coaxial transmission line with a (50 ohm) RG-8/U or LMR-400 Ultraflex cable.** Amateur radio equipment typically has a 50-ohm impedance. Replacing a 75-ohm RG-59/U cable (which would cause an impedance mismatch and signal loss) with a 50-ohm cable like RG-8/U or LMR-400 Ultraflex would *improve* the impedance match between the radio and the antenna system. This would reduce transmission line loss and result in *improved* overall system sensitivity, not a loss.