Answer: A) They have been geographically isolated from each other for a longer time.
Explanation: An isthmus is defined as a narrow strip of land that separates two bodies of water as well as connecting two larger landmasses at the same time. Thus, an isthmus if an efficient physical barrier that has separated an original shrimp species. This has resulted in the extant deep-water shrimp species through the evolutionary process known as allopatric speciation.
The age of an isthmus is in the range of at least two million years. Thus, the two deep-water shrimp species have been separated from each other for a very long time.