In the following sentence completion question, choose the most appropriate word to fill in the blank: As the only ________ person in the wacky family, the sensible girl felt like the odd woman out.

Introduction / Context:
This question tests the ability to choose the correct adjective that fits logically and semantically into a sentence. The sentence contrasts the sensible girl with the rest of her “wacky family”. The blank must be filled with a word that emphasises her mental stability and reasonableness in contrast to the others.

Given Data / Assumptions:
- The family is described as “wacky”, suggesting they behave in an odd or eccentric way. - The girl is described as “sensible”. - The blank is followed by “person in the wacky family”. - The phrase “odd woman out” implies that she is different from everyone else in a particular respect.

Concept / Approach:
The context strongly suggests a contrast between the girl and the rest of the family. The rest of the family is wacky, so she must be normal, reasonable, or mentally sound. In English, the adjective “sane” means mentally sound, sensible, or reasonable. Therefore, “sane person” is the natural counterpart to a “wacky family”. Other options either have negative meanings or do not match the context.

Step-by-Step Solution:
Step 1: Identify the key contrast: “wacky family” versus “sensible girl”. The girl is being contrasted with the family in terms of mental behaviour. Step 2: Note that the blank describes the girl: “As the only ________ person in the wacky family ...”. The adjective must match “sensible”. Step 3: Consider “sane”. This means mentally sound or reasonable. “Only sane person” fits with “sensible girl” and naturally contrasts with “wacky family”. Step 4: Consider “insane”. This means mentally unsound or crazy, which would not match “sensible girl”. Step 5: Consider “vain”. This refers to excessive pride in one's appearance or achievements, which is unrelated to being sensible or wacky. Step 6: Consider “main”. This is an adjective meaning primary or chief, which does not fit well with “odd woman out”. Step 7: Consider “plain”. This means simple or not beautiful, which again does not capture the contrast in mental behaviour implied by “wacky” and “sensible”.

Verification / Alternative check:
Insert each option into the sentence and read it aloud. “As the only sane person in the wacky family, the sensible girl felt like the odd woman out” sounds natural and coherent. The other combinations either contradict the idea of her being sensible or introduce unrelated qualities. This confirms that “sane” is the only choice that properly expresses the intended contrast.

Why Other Options Are Wrong:
Insane: Opposite of “sane” and contradicts the description “sensible girl”. Vain: Refers to vanity, not mental stability or reasonableness. Main: Means primary or most important, but does not explain why she feels like the odd woman out. Plain: Refers to appearance or style, not to mental balance or behaviour.

Common Pitfalls:
Sometimes students pick words based loosely on sound or familiarity rather than precise meaning. For example, they may select “plain” because it seems to suit “odd woman out” superficially. To avoid such errors, focus on the exact nature of the contrast in the sentence. Here the contrast is between wacky behaviour and sensible behaviour, which clearly points to “sane”.

Final Answer:
The correct word to complete the sentence is sane.