Step 1: Analyzing the Correct Option
The correct option here is "both", as it refers to two or more individuals and indicates that they have been involved together.
Step 2: Evaluating the Other Options
- "Much" (Option B) would not fit because it is used for uncountable nouns.
- "Each" (Option C) refers to individual entities, but in this case, it implies separate actions rather than joint participation.
- "Enough" (Option D) does not fit grammatically in this context as it is used to express sufficiency, not quantity.
Step 3: Conclusion
Thus, the correct sentence is: "Both employees have been closely associated with the organisation for some time."