49. Which of the following statements explains why sulfonamides are effective antibiotics? (A)serve as analogs of p-aminobenzoic acid and block bacterial synthesis of folate (B) act as inhibitors of bacterial dihydrofolate reductase, thus preventing production of tetrahydrofolate (C)act as suicide substrates for the enzyme dihydropteroate synthetase (D)do not affect humans because folate is a vitamin (E)both a and d are correct