Question 431417

c is correct.
a & b are not correct.
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b has the wrong denominator.
The den has the wrong structure, it has to be a product of the 2 given DENs.
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a has the wrong numerator.
The DEN in a is correct, but the NUM is not correct.  It's not correct because it doesn't match c, which is correct.
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"why it's not correct" is answered without the need for counter examples.
If the problem stated prove it's not correct, or demonstrate that it's not correct, then a counter example would accomplish that.
But, why it's not correct can be answered with "because it's wrong."