Barry was on an antibiotic, but after he took all of it, he had a rash and the doctor prescribed him an antihistamine. which most likely describes what happened to barry? he had a viral infection, but then developed an allergy to the antibiotic. he had a parasite infection, but then it developed into a bacterial infection. he had a fungal infection, but then it developed into a viral infection. he had a bacterial infection, but then developed an allergy to the antibiotic.

He had a bacterial infection, but then developed an allergy to the antibiotic.

He had a bacterial infection, but then developed an allergy to the antibiotic.

Antibiotics are chemical substances which contains biological agents like bacteria, to fight against bacteria already present in the body causing diseases. Overdose of antibody can cause allergies. Antihistamines are drugs which are given for treatment of common allergy symptoms such as sneezing,  running nose, rashes and watery eyes.

In the given condition the overdose of antibiotic has resulted in rash, for treatment of rashes doctor has prescribed him antihistamine. Therefore, statement he had a bacterial infection, but then developed an allergy to the antibiotic describes what happened to Barry.  

the answer is b.) hydrogen bonds between bases.