I believe the question is something like this:
Scientists have identified an asteroid, 2000 BF 19, 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 planet wide 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 plant tremendous damage, but it would
E. and that, if it strikes Earth, it could experience a tremendous amount of damage but
First of all we need to realize that, since all the options start with
and, we need parallelism in the sentence.
and in the original sentence is a parallel connector, so we need the structure
"that... and that.." - (X and Y) in the sentence. So options A and B are ruled out.
Lets check C , D and E now.
We can rule out D because
"if Earth is struck by it" is passive and awkward construction. We need this part of the sentence in subjunctive tense because it represents a hypothetical condition.
We rule out E because, although E uses
that after
and, it still doesn't maintain the parallelism, since
that is not followed by a verb as done in the first part of the sentence. Subjunctive tense is also missing.
The correct answer C maintains the required parallelism and correctly uses the required subjunctive tense -
"if it were to strike Earth"
Observe the parallelism in C. Notice that both
that are followed by a verb.
Scientists have identified an asteroid, 2000 BF 19, that is about half a mile wide (X) and that, if it were to strike Earth, could do tremendous damage to part of the planet (Y) but would probably not cause planet wide destruction.
that is about half a mile wide (X)
that could do tremendous damage to part of the planet (Y)
X and Y are both parallel here. So construction "X and Y" is grammatically correct in C.
There is another internal parallelism maintained in C that we need to check.
but at the end of option C is also a parallel connector. So we need to make sure that in "X but Y" construction, both X and Y are parallel.
Notice in C,
could do tremendous damage to part of the planet (X)
would probably not cause planet wide destruction (Y)
X and Y are both parallel here. So construction "X but Y" is grammatically correct.
Hope that helps..
