Your friend was diagnosed with strep throat 2 months ago. She was treated with antibiotics for 10 days, but two weeks after treatment, the symptoms returned. She was given a different antibiotic and her symptoms improved again, initially, but then got worse. What is happening?

A) Your friend has taken antibiotics so long that she has become tolerant to them, making them ineffective.
B) Exposure to antibiotics has caused each individual bacterial cell to evolve resistance to the antibiotics.
C) Your friend was originally infected with some bacteria that were resistant to these two antibiotics and the bacteria multiplied.
D) Your friend probably doesn't have a bacterial infection. There must be some other reason for her symptoms.