Earth strikes

[mgmt_gmat]

Scientists have identified an asteroid, 2000 BF19, that is about half a mile wide and, if it
strikes Earth, it can do tremendous damage to part of the planet but probably not cause
planetwide destruction.
A. and, if it strikes Earth, it can do tremendous damage to part of the planet but
B. and, if it would strike Earth, part of the planet could experience a tremendous
amount of damage but it would
C. and that, if it were to strike Earth, could do tremendous damage to part of the
planet but would
D. and that, if Earth is struck by it, can do part of the planet tremendous damage, but
it would
E. and that, if it strikes Earth, it could experience a tremendous amount of damage
but
Answer:
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[vijay_venky]

My pick C.
Initially thought A as the conditional looked fine, but the verb to be is not there after "but" and C rightly introduces it.