Final answer:
The correct answer is A) User-level Thread, which refers to threads managed by a threading library at the user level, without the necessity of privileges, and can be oblivious to multiprocessing benefits.
Step-by-step explanation:
The question relates to the types of threads used in operating systems. User-level threads are threads that are managed by a threading library at the user level, don't require privileges for their operations, and are not aware of multiprocessing benefits since they are not managed by the kernel. A system call from a user-level thread can indeed be blocked, but the entire process may not block if it has multiple threads. Kernel-level threads, on the other hand, are managed by the operating system kernel, which allows them to take advantage of multiprocessing. Therefore, the correct answer would be A) User-level Thread.