Introduction:
In this scenario, A, a contractor, has appointed B to manage his entire work. The agreement states that B will receive 50% of the profits as his remuneration and will bear all the losses, if any. To determine the role of B in this situation, let's examine the options provided.

The Options:
A: A's partner
B: A's agent
C: Sole proprietor
D: None of these

Analysis:
To determine the correct option, we need to understand the legal relationship between A and B based on the given information.

1. A's Partner:
A partnership involves a legal relationship where two or more individuals carry on a business together and share its profits and losses. In this scenario, B is not presented as a partner of A but rather as someone appointed to manage A's work. Therefore, B cannot be classified as A's partner.

2. A's Agent:
An agent is a person who acts on behalf of another (the principal) and has the authority to make legal decisions and enter into agreements on the principal's behalf. In this case, B is appointed by A to manage his work, indicating an agency relationship. B acts as A's representative and makes decisions regarding the work. Therefore, B can be classified as A's agent.

3. Sole Proprietor:
A sole proprietor is an individual who owns and operates a business alone, assuming all profits and losses. In this scenario, A appoints B to manage his work, indicating that A is the sole proprietor. B is not the owner of the business but rather the manager, so B cannot be classified as a sole proprietor.

Conclusion:
Based on the analysis, the correct option is B: A's agent. B acts as A's representative and manages the work on A's behalf. B receives remuneration based on a percentage of the profits and bears all the losses, making B an agent rather than a partner or sole proprietor.