Imagine you're executing the top-down implementation of the merge sort algorithm in ascending order on the array: [12, 4, 3, 9, 5]. After several recursive calls and splitting, you reach the point where you need to merge two subarrays: [4, 12] and [3, 5, 9]. In the process of merging these subarrays, which element will be the first to be moved to the sorted array?
If the situation where these two subarrays are merged doesn't arise, or if it's impossible to determine such a situation, then indicate it by writing .
Tip: Visualizing the process using a pen and paper can help you understand the steps involved.