Reasons for re-emergence of microbial diseases...

Could someone help me with a homework question I have? I have tried looking it up in my textbook but I can't seem to find the answer (I think I have been in the book for so long I can't make sense of it). The book I am using is Microbiology an Introduction, tenth edition by: Tortora, Funke, Case. Chapter 14 and as far as I know it should be on page 416. I would appreciate any help! Here is the question:

Select the reasons for re-emergence of microbial diseases. (Select all that apply.)

A. infectious agents mutate or evolve into more deadly strains against which humans have little resistance.
B. Mass migrations of refugees bring infectious diseases into new areas.
C. Global travelers visiting exotic areas bring new diseases home with them.
D. Growth of congested urban slums, lacking sanitation and clean water
E. Over time, animal infections can become transmissible to humans