Why are many bacterial infections more difficult to treat now than they were fifty years ago?

Responses
A Because there are more types of bacteria now.Because there are more types of bacteria now.
B Because bacteria have evolved resistance to antibiotics.Because bacteria have evolved resistance to antibiotics.
C Because bacteria reproduce at greater rates than in the past, since there are more people on earth.Because bacteria reproduce at greater rates than in the past, since there are more people on earth.
D Because treatment of virus infections consumes many antibiotics that were formerly used only for bacteria.

B Because bacteria have evolved resistance to antibiotics.