Final answer:
When someone is blundering about in the dark, they are moving clumsily due to poor visibility. Blundering suggests mistakes are made because it is difficult to see, leading to stumbling and potential disorientation.
Step-by-step explanation:
If someone is blundering about in the dark, it means that they are lost and stumbling because of poor visibility. The term 'blundering' implies making mistakes or moving clumsily, often without a clear sense of direction or purpose due to the lack of light. When there is inadequate light, as at midnight for instance, it becomes difficult to see and navigate. In such a scenario, a person could easily make missteps and have trouble finding their way.
Imagine a person in the woods where the lack of adequate lighting could very well lead to uncertainty in movement, causing them to trip over unseen roots or bump into trees. Similarly, someone walking in a low-light environment in an urban setting might find themselves disoriented and anxious, potentially leading to a sense of fear, much like someone startled by footsteps in the dark might feel.
Therefore, the right answer to the original question is that if someone is blundering about in the dark, what is happening is (b) They are lost and stumbling due to poor visibility.