In this idiom and phrase question, select the option that best expresses the meaning of the expression Through thick and thin when describing a relationship or support.

Introduction / Context:
This question tests your understanding of a common English idiom, Through thick and thin. Idioms are fixed expressions whose meanings cannot always be guessed from the individual words. They play an important role in spoken and written English because they convey ideas in a vivid and memorable way. Knowing the correct meaning of popular idioms helps you understand texts more accurately and express yourself more naturally in the language.

Given Data / Assumptions:

• The idiom is: Through thick and thin.
• The options suggest different possible interpretations related to circumstances, obstacles, and physical changes.
• The idiom is often used to describe loyalty, relationships, or support.
• We assume the context is positive and refers to remaining loyal despite difficulties.

Concept / Approach:
Through thick and thin is a well established idiom that means to remain loyal and supportive under all conditions, whether good or bad, easy or difficult. The words thick and thin symbolise different types of circumstances: thick stands for hard times and thin for easier times, or vice versa. The phrase emphasises consistency and commitment rather than merely facing obstacles. Therefore, the correct option must capture the idea of staying together or remaining supportive regardless of changing situations.

Step-by-Step Solution:
Step 1: Recall the standard meaning of the idiom. Through thick and thin means staying with someone or something in all situations, good or bad. Step 2: Examine option a, To be together under all circumstances, no matter how difficult. This directly matches the idea of unwavering loyalty and support. Step 3: Examine option b, None of the days are alike, some are good and some are bad. This describes variation in life but says nothing about loyalty or staying together. Step 4: Examine option c, To pass through various types of obstacles. This focuses on facing obstacles but does not clearly mention staying loyal or together with someone. Step 5: Examine option d, An obese person suddenly losing weight. This is unrelated to the idiom and clearly incorrect. Step 6: Examine option e, To support someone only in good times, which is the opposite of the intended meaning, since through thick and thin emphasises support even in bad times. Step 7: Option a is the only choice that highlights being together under all circumstances, which is exactly what the idiom conveys.

Verification / Alternative Check:
To verify, consider typical sentences that use the idiom. For example, They remained friends through thick and thin means that they stayed close friends even when life was difficult. Another example, She stood by her family through thick and thin, emphasises loyal support in both good and bad times. In each case, the idiom does not simply describe facing obstacles but also highlights commitment and loyalty. Comparing these uses with the options confirms that option a is the correct interpretation.

Why Other Options Are Wrong:
Option b only states that some days are good and others are bad, without any mention of staying together or showing loyalty.
Option c talks about passing through obstacles, which can occur even without loyalty or relationships, so it does not express the full meaning of the idiom.
Option d relates to physical weight loss and is completely unrelated to the idiom.
Option e contradicts the meaning by limiting support to good times, whereas the idiom specifically includes difficult times as well.

Common Pitfalls:
Learners sometimes pick options that mention difficulties or obstacles and overlook the key idea of constant support. While obstacles are part of the picture, the essence of through thick and thin is unwavering loyalty, not just surviving hardships. Another pitfall is interpreting idioms too literally, reading thick and thin as physical descriptors rather than metaphorical references to changing circumstances. To excel in idiom questions, it is important to learn idioms as complete units with their established meanings rather than trying to interpret them word by word.

Final Answer:
The idiom Through thick and thin means to be together under all circumstances, no matter how difficult, so option a is correct.