When the physical geographical features like mountain or the rivers serves to divide or distinct two political border are termed as the natural boundary.
Answer: Option A
Step-by-step explanation:
The natural boundary is defined by the barriers occurring natural as geographical feature to divide two distinct zone or state serving for the political boundary.
This is done in order to avoid the division of the geographical feature. Political boundaries are thus formed between any two countries or any two states along the geophysical boundary.