Which of the Following Is a Proximal Cause That Will

Which of the following is a proximal cause that will stimulate birds to migrate?

A) environmental stimuli such as changes in temperature
B) the bird getting older
C) an increase in the number of males within the population causing an increase in competition for mates
D) a new predator moving into the environment that poses a threat to the survival of the population
E) All of these are proximal causes that will influence birds to migrate.