1. Correct Answer
     The correct answer is Option C: 24.
 2. Explanation
     To solve this problem, we need to determine the number of ways to arrange 4 horizontal stripes using the colors red, green, and yellow such that no two adjacent stripes have the same color.
     Let's break down the problem step by step:
     1. Choosing the color for the first stripe:
            ○ We have 3 options for the first stripe: red, green, or yellow.
     2. Choosing the color for the second stripe:
            ○ The second stripe cannot be the same color as the first stripe. Therefore, we have 2 options for the second stripe.
     3. Choosing the color for the third stripe:
            ○ The third stripe cannot be the same color as the second stripe. Again, we have 2 options for the third stripe.
     4. Choosing the color for the fourth stripe:
            ○ The fourth stripe cannot be the same color as the third stripe. We have 2 options for the fourth stripe.
     Now, we calculate the total number of ways to arrange the stripes:
     \[
     \text{Total ways} = (\text{ways to choose first stripe}) \times (\text{ways to choose second stripe}) \times (\text{ways to choose third stripe}) \times (\text{ways to choose fourth stripe})
     \]
     \[
     \text{Total ways} = 3 \times 2 \times 2 \times 2 = 24
     \]
     Therefore, the number of different ways to design the flag with the given conditions is 24.