The last ice age primarily affected human migration in the following way:
A. It created land bridges where ocean had once been.
During the last ice age, lower sea levels due to the accumulation of ice sheets exposed land bridges, such as Beringia, which connected Asia and North America. This allowed for migration of human populations into new territories. While the other options may have some relevance to human behavior during that time, the creation of land bridges is the most direct consequence of the ice age that influenced migration patterns.