In polluted industrial English cities during the Industrial Revolution, two plant diseases -- black spot, which infects roses, and tar spot, which infects sycamore trees -- disappeared. It is likely that air pollution eradicated these diseases. Which one of the following, if true, most strengthens the reasoning above?
A: Scientists theorize that some plants can develop a resistance to air pollution.
B: Black spot and tar spot returned when the air in the cities became less polluted.
C: For many plant species, scientists have not determined the effects of air pollution.
D: Black spot and tar spot were the only plant diseases that disappeared in any English cities during the Industrial Revolution.
Choose A, B, C or D as your solution.
B