Correct Option (2)
The passage explicitly states, "Losing his way in a smoke-filled passage, he missed the stairway and went into another room." This sentence directly establishes the cause-and-effect relationship: the presence of smoke in the passage led to his disorientation, which in turn caused him to miss the stairway and enter an alternative room.
Incorrect Options:
Option 1: "he did not know where exactly the stairway was." This describes a consequence of his disorientation, which was primarily caused by the smoke-filled environment, rather than the fundamental reason for entering a different room. The inability to locate the stairway is an effect, not the initial cause of his deviation.
Option 3: "he was extremely nervous." The provided text does not mention the man's emotional state as a reason for his actions. Attributing his entry into another room to nervousness is an inference not supported by the narrative.
Option 4: "he stumbled on a bundle." This event occurred chronologically after the man had already entered the room. Stumbling on the bundle is a subsequent action within the room, not the reason for his initial entry into it.