a. human population growth/overpopulation/urbanization;
b. hunting / overfishing/ overharvesting;
c. loss of natural habitat by natural disasters
OR
climate change/global warming;
d. pollution by burning of fossil fuels;
e. pollution of land/water by use of fertilizers/pesticides/chemicals / acidification of oceans;
f. spread of pests/diseases/invasive alien species;
b: Accept other forms of over-exploitation.
c: Accept an example of natural disaster or loss of habitat.
d and e: Do not accept "pollution" without any further details.