System calls are made with: a) A system thread b) A thread created and managed by CSRSS c) The app's thread d) A kernel thread created upon process start

The option (d) is correct

Explanation:

Solution

System calls are made with a: Kernel thread created upon process start

A computer program request service from a kernel using System calls. It is a kernel thread which is created when a process starts. System calls allows services of the operating system to the user program between the   Application programming interface (API).

A kernel thread: refers to processes and interfere or stops handlers; it is the entity managed by the system scheduler. A kernel thread moves inside an operation, but can be called by any other instructions (execution) in the system.