单项选择题

The author is primarily concerned with

A． criticizing Ellison on the basis of reactionary assumptions his work makes about politically-involved blacks
B． exposing the limitations of Ellison's novel when compared with the actual work performed by black workers and activists
C． chronicling the effects Ellison's novel had upon the black activist movements of the 1960's
D． comparing Ellison's view of post-industrial black America with that of the activists working at the time
E． critically describing Ellison's approach as novelist to the task of ethical publicity

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单项选择题

The discussion of the means by which GHBs escape black holes that is offered in the second paragraph suggests that which of the following must be assumed if the conclusions described in lines 3 - 5 are to he validly drawn

A． The light emissions from GHBs always degrade from gamma rays to x-rays to visible light and, finally, to radio waves.
B． Particles in GHBs include not only photons but electrons and their antimatter counterpart, positrons.
C． The expansion of a fireball as it moves away from the black hole lowers photon density.
D． Shock waves almost always form at the boundary between the fireball and the external medium.
E． The timescale by which we witness astronomical phenomenon is always ruled by the principles of relativity.

单项选择题

The passage suggests that scientists consider their understanding of gamma-bursts to be

A． incomplete because they still have yet to establish a taxonomy of the various types of GHBs they have observed
B． adequate enough to redirect research toward other more perplexing aspects of black holes
C． unsurprising, given that scientists have long felt kinetic energy to play a role in the emergence of GHBs
D． disappointing because the mechanism by which GHBs become visible is still poorly understood
E． in need of confirmation through comparison with another astronomical phenomenon that involves electromagnetic bursts