In the following question, a blank is given in the sentence: "_____ you work hard, you cannot succeed." Select the conjunction that best completes the sentence to express a necessary condition for success.

Introduction / Context:
This question tests your understanding of conjunctions that introduce conditions. The sentence states that success is impossible without hard work. You must select the word that most clearly and concisely expresses a negative condition, that is, that the absence of hard work will prevent success. Choosing the right conjunction ensures that the logical relation between effort and success is correctly conveyed.

Given Data / Assumptions:

• Sentence: _____ you work hard, you cannot succeed.
• Options: If, Till, Until, Unless.
• The second clause you cannot succeed is negative and expresses impossibility.
• The intended meaning is that success is impossible if you do not work hard.

Concept / Approach:
Unless is a conjunction meaning except if or if not. When you say Unless you work hard, you cannot succeed, you state that the only way to avoid failure is to work hard. This matches the common motivational statement about hard work and success. If is a general conditional conjunction that can be used with either positive or negative second clauses, but If you work hard, you cannot succeed changes the meaning and becomes incorrect. Till and until are time conjunctions, used to talk about something happening up to a particular point in time, not about conditions for success. Therefore, unless is the most appropriate choice.

Step-by-Step Solution:
Step 1: Interpret the meaning: the sentence is saying that without hard work, success is not possible. This is a negative condition. Step 2: Consider unless, which explicitly means if not. Unless you work hard can be paraphrased as if you do not work hard. Step 3: Insert unless into the sentence: Unless you work hard, you cannot succeed. This matches the intended idea perfectly. Step 4: Test if. If you work hard, you cannot succeed would wrongly suggest that hard work results in failure, the opposite of the intended meaning, so if cannot be used here. Step 5: Test till and until. Till you work hard, you cannot succeed and Until you work hard, you cannot succeed are unidiomatic and blur time and condition; they suggest waiting until you start working hard, not a general rule about success. Step 6: Therefore, unless is the only conjunction that naturally introduces the required negative condition.

Verification / Alternative check:
Rewrite the sentence with an explicit negative condition: If you do not work hard, you cannot succeed. This is a clear statement. Now replace If you do not with Unless you and remove the negative in the subordinate clause: Unless you work hard, you cannot succeed. The two sentences are equivalent in meaning. This shows that unless is the intended conjunction here. None of the other options allow such a clean transformation.

Why Other Options Are Wrong:
If is used for general conditions but would require a different main clause to keep the meaning positive, such as If you work hard, you can succeed, which is not what is printed in the question.

Common Pitfalls:
Some learners treat unless as interchangeable with until because both start with the same two letters, but they belong to different categories: unless is a conditional conjunction, while until or till indicates time. Another mistake is to place unless in the main clause and keep a negative subordinate clause, causing a double negative. The safe pattern to remember is Unless plus positive condition, followed by a negative result clause, as in Unless you study, you will not pass. The given sentence follows that exact pattern.

Final Answer:
The sentence is correctly completed as Unless you work hard, you cannot succeed.