Answer: Red ribbon.
Explanation:
When it comes to fractions, if all the fractions being compared have the same numerator, the fraction with the smallest denominator is the largest.
In this question, all the fractions have a numerator of 1 so the longest one will be the one with the smallest denominator which is 1/3. The red ribbon is the longest.
Another way is to convert them to percentages:
1/6 * 100% = 16.7%
1/3 * 100% = 33.3%
1/4 * 100% = 25%
Red ribbon is again the largest.