Final answer:
The largest river stream order that exists among the given options is d. 12. This follows the Strahler Stream Order Classification system, where high stream orders like 12 are associated with the world's largest rivers such as the Amazon.
Step-by-step explanation:
The question asks about the largest river stream order that exists. In fl_vial geomorphology, the stream order is a measure of the hierarchy of streams from the source (headwaters) to the river's mouth. Stream orders are part of the Strahler Stream Order Classification system, which is a method used to define the size and complexity of a river system. According to this system, when two streams of the same order meet, they form a stream of the next highest order, but when streams of different orders meet, the highest order prevails.
The largest rivers, such as the Amazon, the Nile, and the Mississippi, have high stream orders. The Amazon River, for example, is considered to have a stream order of 12. Options within the question suggest possible stream orders from 5 to 13. It's worth noting that stream orders can potentially go higher depending on the complexity of the river system, but the highest commonly recognized in literature is the 12th order, which is associated with the world's largest rivers.
Thus, the correct answer, which is the largest river stream order that exists among the given options, would be d. 12.