In this idioms question, select the alternative that best explains the meaning of the expression "up a blind alley" as it is used in everyday English.

Introduction / Context:
The idiom "up a blind alley" is commonly used in English to describe a course of action that is pointless or leads nowhere. It suggests that someone is putting effort into an approach that cannot succeed, similar to walking into a dead end street where there is no way through. Understanding such idioms is essential for interpreting newspaper articles, essays, and exam passages correctly.

Given Data / Assumptions:

• The idiom given is "up a blind alley".
• The options describe various ideas, including hiding something, not warning someone, taking risks, following an action leading to a bad outcome, and trying at something that cannot succeed.
• You must select the explanation that best matches the established idiomatic meaning.

Concept / Approach:
A blind alley is literally a street that has no exit at the far end; you can walk in but you must come back out the same way. Metaphorically, being "up a blind alley" means pursuing a line of action, investigation, or reasoning that will not produce any useful result. The emphasis is on the fact that the chosen approach will not lead to the desired outcome, no matter how much effort is put in. Therefore, the meaning must relate to an unsuccessful or wrong direction rather than general danger, secrecy, or love of thrills.

Step-by-Step Solution:
Step 1: Focus on the image of a dead end or blind alley, which suggests no way forward. Step 2: Read option D: "following a course of action that is certain to lead to an undesirable outcome". This describes going down a path that will not end well, which matches the idiom well. Step 3: Read option E: "trying hard at something that cannot possibly succeed". This is also close to the idea, but it focuses more on the effort and less on the mistaken course of action. Step 4: Compare D and E. Option D captures both the notion of a path and the inevitability of an undesirable result, which is more precise. Step 5: Option A, "hiding something intentionally", and option B, "not warning a person in danger", have no connection to dead ends or failed paths. Step 6: Option C about enjoying thrills through risk taking is unrelated to the idea of a futile or mistaken direction. Step 7: Therefore, option D is the best explanation of the idiom.

Verification / Alternative check:
Consider example sentences: "The police investigation turned out to be up a blind alley" or "If you keep arguing on that point, you are going up a blind alley". In both cases, the focus is on an approach that will not yield useful results. Paraphrasing these as "following a course of action that is certain to lead to an undesirable outcome" is accurate. Option E is close but does not emphasise the idea of a mistaken path as strongly as D does, which is why D is more suitable in the exam context.

Why Other Options Are Wrong:
Option A talks about deliberate concealment and not about a wrong route. Option B concerns failure to warn, which involves inaction rather than pursuing the wrong path. Option C focuses on thrill seeking and risk, which are unrelated to the idiom. Option E is semantically similar but less precise than D because not every impossible task is described as a "blind alley"; sometimes the issue is not that the task is impossible, but that the chosen approach is wrong. Option D captures both the course of action and the inevitable negative result.

Common Pitfalls:
Candidates may choose an option that seems dramatic or negative without matching it closely to the imagery of an alley with no exit. Another mistake is to confuse "blind alley" with "turning a blind eye", which has a different meaning (deliberately ignoring something). To avoid such confusions, always picture the literal image behind the idiom and then relate it to the situation described in the options.

Final Answer:
"Up a blind alley" means following a course of action that is certain to lead to an undesirable outcome.