CONSTRAIN:

A． A historical theory is sketched and a problem with the theory is cited.
B． Evidence for an objection to a theory is mentioned and a generalization from that evidence is advanced.
C． A paradox about the origins of a historical phenomenon is pointed out and the author's explanation of the paradox is expounded.
D． A statement about a historical phenomenon is offered and a possible misinterpretation of that statement is addressed.
E． A new explanation for a historical phenomenon is given and evidence for that explanation is provided.

A． The results of geographical survey prove that no crater larger than twelve kilometers exists on the surface of Mars.
B． Fragments from smaller impact events on Mars are highly unlikely to survive entry through the Earth's atmosphere.
C． The velocity of rocks escaping from Mat's gravity is greater when they have been loosened by a large impact.
D． Huge impacts on Mars are proven to be less rare than was previously thought.
E． A double-succession of large impacts is found to have occurred on Mars in a relatively short period of time.