You have identified two nutritional mutants in a new species of yeast that are unable to live on minimal media but can both live on media supplemented with pyruvate. flipping through your biol 61 textbook, you see that a precursor to pyruvate in glycolosis is phosphoenolpyruvate (pep), which is converted to pyruvate through the action of pyruvate kinase. your first mutant strain can grow on either pep or pyruvate, but your second mutant strain can only grow on pyruvate and not on pep. this suggests:

Two nutritional mutants have been identified in a new species of yeast, which are not able to thrive on minimal media, however, both of them can live on media added with pyruvate. It has been witnessed that mutant strain 2 does not possess the tendency to grow in the existence of PEP. This shows that it does not comprise the enzyme that transforms PEP to pyruvate.  

However, on the other hand, the mutant strain 1 possesses the tendency to grow in the existence of PEP and it also possesses the enzyme that transforms PEP to pyruvate. Therefore, second strain exhibits a mutation in pyruvate kinase, while mutation in strain 1 is found in some other gene, that is, apart from pyruvate kinase.  

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b is the best answer for this question.