Ticks attach themselves to host animals to feed. Having fed to capacity, and not before then, the ticks drop off their host. Deer ticks feeding off whitefooted mice invariably drop off their hosts between noon and sunset, regardless of time of attachment. White-footed mice are strictly nocturnal animals that spend all daytime hours in their underground nests. Which one of the following conclusions can be properly drawn from the statements above? ['Deer ticks all attach themselves to whitefooted mice during the same part of the day, regardless of day of attachment.', "Deer ticks that feed off white-footed mice drop off their hosts in the hosts' nests.", 'White-footed mice to which deer ticks have attached themselves are not aware of the ticks.', 'Deer ticks sometimes drop off their hosts without having fed at all.']