Between 2005 and 2050, population is expected to continue growing in all of the following world regions except
a. africa
b. asia
c. europe
d. north america

It's definitely not Asia and not Africa; the population is expected to grow in Asia and in Africa. 

both Europe and North America are possible options: they have all the necessary requirements for a lack of population growth: education of women, family planning, good financial situation. 

However, I expect North America to have  a bigger population growth than Europe (due to both Emigration and birth rate), 

So the best answer is : Europe.