When the first antibiotics became available in the late 1940s and early 1950s, these antibiotics were effective against all bacterial infections. today however, there are a multitude of antibiotic resistant bacterial infections. what conclusion can be drawn? a) antibiotics of today are not as strong as those in the past. b) antibiotics cause dna mutations in bacteria, and over time, this has led to resistance. c) over time, bacteria have turned into viruses, and antibiotics have no affect over viruses. d) bacteria have become resistant to antibiotics over time due to evolution by means of natural selection.