Small experimental vacuum tubes can operate in heat that makes semiconductor components fail. Any component whose resistance to heat is greater than that of semiconductors would be preferable for use in digital circuits, but only if that component were also comparable to semiconductors in all other significant respects, such as maximum current capacity. However, vacuum tubes' maximum current capacity is presently not comparable to that of semiconductors. If the statements above are true, which one of the following must also be true? ['Vacuum tubes are not now preferable to semiconductors for use in digital circuits.', 'Resistance to heat is the only advantage that vacuum tubes have over semiconductors.', 'Semiconductors will always be preferable to vacuum tubes for use in many applications other than digital circuits.', 'Once vacuum tubes and semiconductors have comparable maximum current capacity, vacuum tubes will be used in some digital circuits.']