The correct answer is option 'C': Two weeks.

Explanation:
Aram and Mourad kept the stolen horse for two weeks. Let's break down the details to understand why this answer is correct.

1. Introduction:
- Aram and Mourad are the two individuals who are involved in this situation.
- They have stolen a horse.

2. Context:
- The context is not explicitly mentioned in the question, but we can assume that Aram and Mourad stole the horse for some reason.
- It could be for their personal use, to sell it, or for some other purpose.

3. Time Period:
- The question asks about how long Aram and Mourad kept the stolen horse.
- The options provided are one day, one week, two weeks, and three weeks.

4. Elimination Process:
- We can eliminate options 'A' (one day) and 'D' (three weeks) based on the given information.
- The question states that they kept the horse for a longer duration than one day, but not as long as three weeks.

5. Analysis:
- This leaves us with options 'B' (one week) and 'C' (two weeks).
- We need to determine which option is correct based on the available information.

6. Final Answer:
- The correct answer is option 'C': Two weeks.
- This means that Aram and Mourad kept the stolen horse for a period of two weeks.

Overall, based on the given information, the stolen horse was kept by Aram and Mourad for a duration of two weeks.