The correct answer is A: Set the squelch threshold so that receiver output audio is on all the time. To hear a weak FM signal, you need to set the squelch threshold so that receiver output audio is on all the time (squelch fully open or turned all the way down). This allows you to hear signals that are below the normal squelch threshold. Squelch mutes the receiver when no signal is present. If squelch is set too high (tight), it won't open for weak signals. To hear weak signals, you need to open the squelch completely (turn it all the way down) so the receiver audio is always on. You'll hear background noise, but you'll also hear weak signals that would otherwise be squelched out. This is the standard technique for weak-signal work on FM.