Explanation:

The sentence is describing the marks obtained in the History test, and it is comparing them to other possible marks. In this case, the highest degree of the adjective is required to indicate the superior quality or level of the marks.

The correct degree of the adjective to use in this sentence is "the best."

Reasoning:

To determine the appropriate degree of the adjective, we should consider the following:
1. Comparative Degree: The comparative degree is used when comparing two things. In this sentence, we are not comparing the marks to anything else, so the comparative degree is not appropriate.
2. Superlative Degree: The superlative degree is used when comparing more than two things and indicating the highest or lowest degree of a quality. In this sentence, the marks are being compared to all possible marks that could have been obtained in the History test, indicating the highest degree of quality. Therefore, the superlative degree is the correct choice.

Options Analysis:

a) The better: This is the comparative degree of the adjective "good." It indicates a higher degree of quality than another option but not the highest degree. This option is incorrect.
b) Best: This is the superlative degree of the adjective "good." It indicates the highest degree of quality. However, the sentence requires the use of the definite article "the" before the adjective to indicate a specific noun (marks). Therefore, this option is incorrect.
c) The best: This is the correct answer. It uses the superlative degree of the adjective "good" and includes the definite article "the" before the adjective to indicate a specific noun (marks).
d) The good: This option uses the positive degree of the adjective "good," which does not indicate a higher or lower degree of quality compared to other options. This option is incorrect.

Conclusion:

The correct degree of the adjective to complete the sentence is "the best" (option c). This choice accurately reflects the highest degree of quality being described in the sentence.

Adjectives are words that modify nouns or pronouns to make them more specific. There are 3 degrees of adjectives: Positive, comparative and superlative. The comparative form of most words is formed by adding '-er' to the original word. The superlative form of the word is formed by adding '-est' to the original word. The word 'the' is used before the superlative degree of words because the superlative degree of the word can indicate one particular thing. In the question given, the sentence talks about 'marks in the history test'.