Final Answer:
one string can be obtained from the other by at most one simple operation is string concatenation. Thus, the correct answer is option a) String concatenation.
Step-by-step explanation:
To determine if one string can be obtained from the other by at most one simple operation, we need to consider the given operations: string concatenation, substring removal, character replacement, and array sorting.
In the case of string concatenation, we can check if one string is a concatenation of the other by simply comparing them. If s + t or t + s is equal to the other string, then they can be obtained from each other by string concatenation.
The other operations involve more complex transformations, such as removing substrings or replacing characters, and may require multiple steps. Array sorting is not applicable to strings as it operates on numerical arrays.
In conclusion, the correct option for determining if one string can be obtained from the other by at most one simple operation is string concatenation (option a). If s + t or t + s is equal to the other string, they can be obtained from each other by a single string concatenation operation.