It can be inferred from the passage that the Cepheid variable method of estimating galacti

c distances would be likely to yield experimentally flawed results in which of the following circumstances？

A．If the luminosity of ordinary stars being compared with that of a Cepheid star were affected by parallax.

B．If the apparent brightness of the Cepheid star being studied required an unusually long period of time to vary.

C．If the gravitational interference surrounding the Cepheid star being observed were more negligible than in most cases.

D．If the Cepheid star being studied existed on the periphery of the universe, at an extremely large distance from the observer.

E．If the Cepheid star being studied were in the same galaxy as the observer.