There is a real ambiguity in the question wording that needs to be cleared away. Until then, both answers are correct, depending on how you look at the question. Reader A naively takes the word "antenna" to be just a simple length of wire, and then locks onto the word "resonance". He then perceives the question to mean the following: If a simple wire is to be an efficient radiator, it must be cut to a resonant length for the operating frequency. Given the reader's misconception, that statement is TRUE. It will remain TRUE to the reader until he recognizes that an antenna is more than just a simple length of wire, and also that a non-resonant length of wire can radiate efficiently when a matching device is part of the antenna system. Reader B recognizes that any practical "antenna" is really an antenna system, so he believes the question is asking the following: If an antenna system is to be an efficient radiator, it must be resonant at the operating frequency. Given this reader's mindset, the answer is TRUE. As many of the responses have already pointed out, a non-resonant length of wire can radiate efficiently if the system is tuned to resonance. Reader C fully appreciates that any practical antenna is really an antenna system, and also knows that any length of wire can radiate efficiently when the system is tuned to resonance. His mind then intuitively concludes that the original author could only have meant to ask the following: If an antenna (system) is to be an efficient radiator, it must be cut to resonance at the operating frequency. That reader will know, with dead certainty, that the correct answer to the question is FALSE, and that is borne out by the original author's explanation. Could the guy who wrote the question have done a better job? Sure! He was a "Reader C"-type who knew just what he meant to ask; he just didn't ask it that way. Did the guy deliberately play with words to trick the readers? Your guess is as good as mine, but I see no evidence of it. So, what do you think? Based on his comments in this thread, does Dan (the OP) fit into one of the three "Reader" categories?