Final answer:
The user process itself initiates a transition into the a. block state when it cannot proceed without an event occurring or a condition being met.
Step-by-step explanation:
The state transition that is initiated by the user process itself is block. When a process cannot continue until some condition is met or some event occurs, it transitions into a block state by executing a system call that makes it wait. This action is typically initiated by the process itself, unlike other transitions which are generally governed by the operating system's scheduler.
For example, when a program is waiting for input from the user or when it requires data that is being read from disk, it might enter a block state voluntarily by invoking an operation that leads to waiting (e.g., read operation on a file). This is comparable to a person standing up from a seated position or a car accelerating while driving, as both actions represent a state change initiated by the respective subjects.