Which one of the following orders presents the correct sequence of the increasing basic nature of the given oxides?

The metallic nature of an element (and hence its basic nature of oxide) increases on descending a group and it decreases along the period. Thus, least basic oxide is ${\mathrm{Al}}_2{\mathrm{O}}_3$ and the strongest basic oxide is ${\mathrm{K}}_2\mathrm{O}$.