In the passage about the quest for a happy life, choose the correct word for the blank: "_____ have attempted to define a happy life in various terms."

Introduction / Context:
In this part of the cloze passage, the author comments on how different people have tried to define what a happy life means. The sentence is: "_____ have attempted to define a happy life in various terms." You must choose the noun that best represents people engaged in philosophical or reflective analysis of life, happiness, and meaning. The passage is not about a narrow academic field but about general human attempts to understand happiness.

Given Data / Assumptions:
- The subject of the sentence is a group of people who propose definitions of a happy life.
- The tone of the passage is philosophical and general, not technical or strictly scientific.
- Options are "Professors", "Thinkers", "Researchers", and "Scientists".
- The next part of the passage mentions "Hedonists", which is a philosophical group, supporting a broader human context rather than a specific profession.

Concept / Approach:
The noun "thinkers" is a general term for philosophers, intellectuals, and reflective people who engage in deep thought about abstract ideas, including happiness. "Professors" and "researchers" are professional designations usually tied to academic institutions or specific fields of study. "Scientists" focus on empirical investigation. Since the sentence talks about defining a happy life "in various terms", the most suitable and inclusive choice is "Thinkers".

Step-by-Step Solution:
Step 1: Identify that the people mentioned are engaged in abstract, philosophical activity rather than in strictly scientific research. Step 2: Evaluate "Professors". They are academic teachers, but the passage is not limited to academic staff. Step 3: Evaluate "Researchers". This suggests structured investigation, often empirical, which is too narrow for the broad philosophical context. Step 4: Evaluate "Scientists". They focus on natural or physical sciences, not primarily on philosophical definitions of happiness. Step 5: Evaluate "Thinkers". This word captures philosophers, writers, and all reflective people who have offered theories about happy living.

Verification / Alternative check:
Read the passage with "Thinkers": "Thinkers have attempted to define a happy life in various terms. Hedonists have a simple notion that happiness lies in the gratification of physical appetites." The sequence now feels natural: first general thinkers, then a particular group (hedonists). Inserting "Scientists" or "Researchers" makes the tone shift toward a technical, empirical discussion, which does not match the philosophical flavour of the later sentences.

Why Other Options Are Wrong:
- "Professors": Too narrow and tied to academic roles; non professors have also shaped ideas about happiness.
- "Researchers": Emphasises formal study rather than broad philosophical reflection.
- "Scientists": Linked mainly with science, not with ethical or philosophical speculation about happiness.

Common Pitfalls:
Candidates sometimes choose a more formal sounding noun like "researchers" or "scientists" because it appears intelligent. However, in cloze tests, you must match the overall tone and subject of the passage. Here the text clearly belongs to moral philosophy, so "thinkers" is the most appropriate and flexible term.

Final Answer:
The correct word is Thinkers, giving the sentence "Thinkers have attempted to define a happy life in various terms."