You are infected with a bacterial disease. Your sister had this same illness last week, and took a full cycle of antibiotics. She quickly became better. You started taking the same antibiotic, but they had no effect. In fact, you had to return to the doctor after a week, because you did not feel better. Why did you remain sick after taking antibiotics, while your sister quickly recovered

Another strain of bacteria must have caused your own sickness

Explanation:

Bacteria are microorganisms that can cause diseases. They exist in different strain (i.e different subtype, though of the same specie).

So, the strain of bacteria that caused illnesses in you and your sister must have been different, and because different strains have unique metabolic machinery, enzymes, and other proteins; the same antibiotics that was effective in curing your sister's bacterial infection would rather be ineffective in your own case.

Thus, your doctor must prescribe a different antibiotic tailored to your bacteria strain

answer; i believe the answer is hydraulic action;

the cell cycle is the final answer! : )