column-width
column-rule
column-float
column-rule-width
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Answer is Wrong!
The correct answer is: D. column-rule-width
The column-rule-width property defines the width of a rule between columns in a multicolumn text flow.
The column-width property defines the width of each column in a multicolumn text flow.
The column-rule property defines the style of the rule between columns in a multicolumn text flow.
The column-float property defines whether or not a column can float.