Explanation:

In note-making during the board examination, students are often allowed to use abbreviations to save time and space. These abbreviations are used to represent commonly used words or phrases. The question asks for the minimum number of recognizable abbreviations that should be used in note-making.

Understanding the question:
The question is asking for the minimum number of abbreviations that should be used. The options are given as "at least one," "at least two," "at least three," and "at least four." We need to determine which option is correct.

Analysis of options:
Let's analyze each option to determine the minimum number of recognizable abbreviations required in note-making.

Option A: At least one abbreviation
If only one abbreviation is allowed, it may not be sufficient for effective note-making. Students may struggle to abbreviate multiple words or phrases and may end up using more space and time. Therefore, option A is not the correct answer.

Option B: At least two abbreviations
With two abbreviations, students have a bit more flexibility in representing commonly used words or phrases. However, it may not be enough to effectively condense the content and save space. Option B is also not the correct answer.

Option C: At least three abbreviations
Three abbreviations provide more opportunities for condensing the content and saving space. It allows students to represent multiple words or phrases in a shorter form. While this may be sufficient for basic note-making, it may still limit the ability to quickly and effectively summarize information. Option C is not the correct answer.

Option D: At least four abbreviations
Option D states that at least four abbreviations should be used in note-making. This provides students with more flexibility and options for condensing information. With four abbreviations, students can represent a greater number of commonly used words or phrases, allowing for more efficient note-taking. Therefore, option D is the correct answer.

Conclusion:
The correct answer is option D, which states that at least four abbreviations should be used in note-making during the board examination. This allows students to effectively condense information and save space while summarizing the content.