In the following sentence, a blank is given which must be filled with the most appropriate word. Select the correct alternative out of the four given options. He could excel in his board exams only after _____ very hard.

Introduction / Context:
Fill in the blank questions check whether you can choose the most suitable word so that the sentence expresses a clear and natural meaning. Here, the sentence describes a student who did well in board exams only after putting in a certain kind of effort. The correct answer must fit both grammatically and in terms of sense, showing the type of hard work needed for success.

Given Data / Assumptions:
- Sentence: He could excel in his board exams only after _____ very hard. - Options: continuing, functioning, learning, toiling. - The blank comes before very hard and must combine naturally with it.

Concept / Approach:
The phrase very hard suggests intense effort or labour. We often use verbs like work, study or toil with this adverbial phrase. The word toil is a verb that means to work very hard, especially over a long period. The present participle toiling is therefore an excellent fit before very hard. Other options like continuing, functioning and learning do not collocate naturally with very hard in this context. They either have different meanings or would require different sentence structures.

Step-by-Step Solution:
Step 1: Understand the context. Excelling in board exams typically requires a lot of hard work and sustained study. Step 2: Consider continuing. To say continuing very hard does not sound natural. Continuing needs an object or complement, such as continuing his studies. Step 3: Consider functioning. Functioning very hard is not a natural expression in English. We usually say functioning normally or functioning properly, not functioning hard. Step 4: Consider learning. Learning very hard is also not a standard phrase. We talk about studying hard or working hard, but learning hard sounds odd. Step 5: Consider toiling. Toiling very hard is meaningful and emphasises hard and often tiring work, which matches the context of exam preparation.

Verification / Alternative check:
Insert each option into the sentence and check the result. He could excel in his board exams only after continuing very hard sounds incorrect. The same is true for functioning very hard and learning very hard. However, He could excel in his board exams only after toiling very hard strongly conveys that he worked extremely hard to achieve that success. The meaning and grammar both fit correctly, confirming that toiling is the appropriate choice.

Why Other Options Are Wrong:
Continuing is wrong because it needs an object or phrase after it and does not combine well with very hard alone in this structure. Functioning is wrong because it is used for operating or working in a mechanical or organisational sense, not for studying or working hard for exams. Learning is wrong because the English phrase is to study hard rather than to learn hard, so the collocation is unnatural.

Common Pitfalls:
Students sometimes choose words that generally relate to study, like learning, without checking whether the exact phrase is idiomatic. Collocations matter a lot in English. Words like work, toil and study collocate naturally with hard or very hard, while words like function or learn do not. To avoid such errors, it is helpful to read widely in English and notice which verbs frequently appear with common adverbs and expressions, especially around work and study.

Final Answer:
The sentence is correctly completed as: He could excel in his board exams only after toiling very hard.