Let's analyze each answer choice:

A. "and, if it strikes Earth, it can do tremendous damage to part of the planet but"

This choice lacks parallel structure. The phrase "it can do tremendous damage" does not match with the subsequent clause "probably not cause planetwide destruction."
B. "and, if it would strike Earth, part of the planet could experience a tremendous amount of damage but it would"

This choice introduces unnecessary conditional phrasing with "if it would strike Earth," which makes the sentence awkward and less concise.
C. "and that, if it were to strike Earth, could do tremendous damage to part of the planet but would"

This choice maintains parallel structure and uses the correct conditional tense ("if it were to strike Earth"). It also conveys the intended meaning clearly and concisely.
D. "and that, if Earth is struck by it, can do part of the planet tremendous damage, but it would"

This choice is awkwardly phrased and lacks parallel structure. The phrase "can do part of the planet tremendous damage" does not match with the subsequent clause "but it would."
E. "and that, if it strikes Earth, it could experience a tremendous amount of damage but"

This choice is awkwardly phrased and lacks parallel structure. The phrase "it could experience a tremendous amount of damage" does not match with the subsequent clause "but."
In summary, choice C is correct because it maintains parallel structure, uses the correct conditional tense, and conveys the intended meaning clearly and concisely. Choices A, B, D, and E are incorrect due to various issues such as lack of parallel structure, awkward phrasing, and incorrect verb tense.

Bernard Baah
MS '05, Stanford
GMAT and GRE Instructor
MapAdvantage Prep