A. More individuals fighting over the same resources
This means there's not enough resources to sustain the population.
C. The loss of the environment in which an organism’s needs are met
This means that the population no longer has a habitat that it can live in, and as the species tries to adjust to it's new environment, it gets killed off.
F. The introduction of new predators into an area
Because it's new, the population doesn't know how to respond to this new threat, and therefore is easy prey.