You are creating an ASP.NET page for a travel service that uses a CheckBoxList control bound to a list of destinations, sorted by popularity rank. The list has three columns, and you want the most popular destination to appear in the top row from left to right at run time. Which CheckBoxList property setting should you use?

Introduction / Context:
ASP.NET list controls such as CheckBoxList can display their items in multiple columns, and the RepeatDirection property determines how items are filled into the rows and columns. When building user interfaces that present ranked data, such as popular travel destinations, it is important that the most popular items appear in the most prominent positions on the page. This question checks your understanding of how RepeatDirection affects the order in which items are rendered in a multi column list.

Given Data / Assumptions:

The page uses a CheckBoxList control bound to a data source containing travel destinations.
Each destination has a popularity rank, and the list is sorted so that the most popular destination appears first in the data source.
The CheckBoxList has RepeatColumns set to three, creating three visible columns for display.
You want the most popular destination to be in the top row, from left to right, as users first see the page.
The question focuses on choosing the correct RepeatDirection property value.

Concept / Approach:
RepeatDirection controls whether list items are filled across rows or down columns. With RepeatDirection.Horizontal and RepeatColumns set to three, the first row will contain the first three items in the data source, in order: item 1, item 2, and item 3. With RepeatDirection.Vertical, items are filled down each column before moving to the next column, which can cause the ranking order to appear in a less intuitive pattern across the top row. If you want the top row to show the highest ranked destinations left to right, you should use RepeatDirection.Horizontal so that items are rendered in row major order.

Step-by-Step Solution:
1. Assume that the data source is sorted by popularity so that destination 1 is most popular, destination 2 is next, and so on. 2. Set RepeatColumns on the CheckBoxList to 3 to create three columns of check boxes. 3. If you choose RepeatDirection.Vertical, the control fills items down the first column (1, 2, 3), then down the second column (4, 5, 6), and so on, which means the top row would display destinations 1, 4, and 7, not the three most popular in order. 4. If you choose RepeatDirection.Horizontal, the control fills items across the first row (1, 2, 3), then the second row (4, 5, 6), which ensures the top row shows the three most popular destinations in correct order. 5. Therefore, to achieve the desired layout, you must set RepeatDirection to Horizontal.

Verification / Alternative check:
You can verify the behavior by building a simple example with nine destinations labeled 1 through 9 and observing how they appear under different RepeatDirection settings. With Vertical, the top row appears as 1, 4, 7, but with Horizontal it appears as 1, 2, 3. This clearly demonstrates that Horizontal is the correct choice when top row order matters.

Why Other Options Are Wrong:
RepeatDirection.Vertical results in the top row containing every fourth item rather than the top three ranked items, so it does not meet the requirement.
RepeatLayout.Flow and RepeatLayout.Table control whether the items are rendered as inline elements or in an HTML table, but they do not change the fundamental left to right versus top to bottom filling behavior for ranking.

Common Pitfalls:
A common mistake is to confuse RepeatColumns with RepeatDirection and assume that specifying three columns alone ensures that the list shows the top three items in the first row. Another pitfall is not testing how the list behaves when the number of items is not a multiple of the number of columns, which can further distort perceived ranking if the settings are incorrect. Always combine correct sorting with the correct RepeatDirection to produce intuitive layouts.

Final Answer:
You should set the CheckBoxList RepeatDirection property to Horizontal so that the most popular destinations appear across the top row.