The correct answer is: B. Less than 18.
A short column is a column whose slenderness ratio is less than 18. A slenderness ratio is a measure of the slenderness of a column and is defined as the ratio of the effective length of the column to the least radius of gyration of the column cross-section.
The effective length of a column is the distance between the points of contraflexure in the column. The least radius of gyration of a column cross-section is the radius of the smallest circle that can be inscribed in the cross-section.
A short column is a column that is not susceptible to buckling. Buckling is a failure mode in which a column collapses under its own weight due to lateral deflection. A short column is not susceptible to buckling because the lateral deflections are small enough that the column does not experience any significant bending moments.
The minimum slenderness ratio for a short column is 18. This means that a column with a slenderness ratio of less than 18 is considered to be a short column.
The options A, C, and D are incorrect because they are greater than 18.