Which of the Following Provides the Best Explanation for the Many

Which of the following provides the best explanation for the many chemical similarities between sodium and potassium?

A) Both have atomic masses between 20 and 40 u
B) Both have an ns¹ electron configuration for their highest occupied energy level
C) Both are main group elements
D) Both are solids at room temperature and pressure
E) The atomic numbers of the two elements differ by less than ten