Your task is to convert each word at an even position to uppercase and return the modified string.

1. Split the input string into an array of words.
2. Create a StringBuilder to build the resulting string.
3. Loop through each word in the array using its index.
4. For each word, check if its index is even.
5. If the index is even, convert the word to uppercase and append it to the result string.
6. If the index is odd, append the word as is.
7. Return the final string after processing all words.