Astronomer: Does a recent meteorite from Mars contain fossilized bacteria? Professor Tagar, a biologist, argues that the bacteria-like structures found in the meteorite cannot be fossilized bacteria, on the grounds that they are one-tenth of 1 percent the volume of the smallest earthly bacteria. However, Tagar' s view cannot be right. Tagar does not accept the views of biologists Swiderski and Terrada, who maintain that Martian bacteria would shrink to one-tenth of 1 percent of their normal volume when water or other nutrients were in short supply. Which one of the following most accurately describes a flaw in the reasoning in the astronomer's argument? ['The argument presumes, without providing justification, that the authorities cited have always held the views attributed to them.', 'The argument presumes, without providing justification, that the opinions of all experts are equally justified.', 'The argument appeals to views that contradict rather than support one another.', 'The argument provides no justification for giving preference to the views of one rather than the other of two competing sets of authorities.']