In English vocabulary, choose the option that best expresses the meaning of the idiom or phrase 'dark horse' used about a contestant or candidate.

Introduction / Context:
Idioms in English often come from colorful images, and 'dark horse' is one such expression that appears in discussions about elections, sports, and competitions. The question asks you to pick the option that best captures what people mean when they call someone a 'dark horse'. Understanding idioms is important in exams because the literal meaning of the words is not enough; you must know the figurative, commonly accepted meaning used in real communication.

Given Data / Assumptions:

Idiom given: 'dark horse'.
Options describe different types of candidates or contestants.
We assume the context is competition, politics, or any contest with winners and losers.
We need the standard dictionary or usage meaning of 'dark horse', not a creative interpretation.

Concept / Approach:
The idiom 'dark horse' originally comes from horse racing. A 'dark' horse is one about which the betting public knows little; its abilities, strengths, or form are not widely known. When such a horse unexpectedly wins, it surprises everyone. In modern usage, the expression was extended to politics, business, and everyday life. It refers to a person or candidate who is relatively unknown or underestimated, but who unexpectedly achieves success or victory. Therefore, we must look for an option that emphasizes both 'little known' and 'unexpectedly wins'.

Step-by-Step Solution:
Step 1: Recall the standard idiom meaning: a relatively unknown competitor who unexpectedly succeeds. Step 2: Check option (a): 'a candidate about whom little is known but who unexpectedly wins'. This exactly reflects the standard explanation and includes both 'unknown' and 'unexpected victory'. Step 3: Check option (b): 'a good person who has been unfairly maligned' focuses on character judgment, not on being unknown. Step 4: Check option (c): 'a person despised by everybody who nevertheless wins' stresses being disliked, which is not the key feature of a dark horse. Step 5: Check option (d): 'a very unpredictable contestant who sometimes wins sometimes loses' refers to inconsistency, not to being unknown and surprising.

Verification / Alternative check:
If you consult standard English dictionaries or usage guides, they define 'dark horse' as a candidate or competitor about whom little is known but who unexpectedly wins or makes a strong showing. There is no emphasis on being hated or on moral goodness; the focus is on surprise and previous obscurity. Reading news headlines or analysis about elections also confirms this: journalists speak of 'dark horse candidates' when someone little discussed in the media suddenly performs very well. This confirms that option (a) is the accurate interpretation.

Why Other Options Are Wrong:
Option (b) associates the idiom with being 'unfairly maligned', which is not part of the idiom's core meaning. Option (c) focuses on being 'despised by everybody', which again is unrelated; a dark horse may actually be liked but simply unknown. Option (d) describes an inconsistent performer who is unpredictable but not necessarily obscure or surprising. None of these capture the central feature of 'dark horse', namely unexpected success by someone previously not much talked about.

Common Pitfalls:
A common mistake is to think 'dark' suggests something negative or evil, leading students to choose options that mention being despised or unfairly treated. Another pitfall is confusing 'dark horse' with 'underdog'. An underdog is expected to lose but might win; a dark horse is not necessarily thought weak, but is simply not widely known. Paying attention to the standard idiomatic meaning, rather than literal word associations, helps avoid these errors.

Final Answer:
The correct answer is: 'a candidate about whom little is known but who unexpectedly wins'.