Choose the option that best expresses the meaning of the idiom "An axe to grind" in the context of hidden motives.

Introduction / Context:
In this question you are asked to interpret the idiom "an axe to grind". This phrase is often used in political discussions, workplace conversations, and media reports to describe people who argue or act not for neutral reasons but because they have some personal stake or hidden agenda. Understanding such idioms is essential for scoring well in English sections of competitive exams.

Given Data / Assumptions:

• The idiom is "an axe to grind".
• The options are "Attack aggressively", "Suffer a lot", "Betray somebody", and "Have a selfish interest".
• The idiom is used in its normal figurative sense, not literally about a physical axe.
• We need to match it with the most accurate meaning.

Concept / Approach:
The origin of the idiom is from the idea of a person who wants to use someone or something simply so that they can sharpen their own axe. Figuratively, it has come to mean that someone is involved in an issue because of personal benefit or grievance, not because of neutral concern. So we must select the option that reflects personal self interest or hidden motive.

Step-by-Step Solution:
Step 1: Recall the standard meaning of "have an axe to grind". It refers to having a private reason, often selfish or biased, for supporting a particular view or action.Step 2: Compare this with the options. "Have a selfish interest" obviously matches this idea of a personal agenda.Step 3: Examine "Attack aggressively". Although the image of an axe might suggest aggression, the idiom itself does not primarily mean attacking, but rather having an interest.Step 4: Examine "Suffer a lot". Suffering may be one result of many situations, but the idiom does not express suffering.Step 5: Examine "Betray somebody". Betrayal is about breaking trust; the idiom does not specifically refer to that.Step 6: Therefore, the only option that accurately captures the idiom is "Have a selfish interest".

Verification / Alternative check:
Consider example sentences: "The councillor has an axe to grind, because the new law will benefit his own business" or "Be careful when listening to their criticism, they have an axe to grind". In these cases, the speaker is warning that the person is motivated by personal benefit, not by fairness. None of the example uses focus on aggression, suffering, or betrayal as the central idea, confirming that selfish interest is the core meaning.

Why Other Options Are Wrong:
Option A, "Attack aggressively", misinterprets the presence of an axe as a weapon and ignores the real idiomatic sense of a personal agenda.
Option B, "Suffer a lot", is unrelated, as the idiom does not refer to emotional or physical suffering.
Option C, "Betray somebody", speaks of disloyalty, which is different from having a hidden motive, even though a person with an axe to grind could possibly betray others; it is not the basic meaning.

Common Pitfalls:
A common error is to focus on the literal image of an axe and assume the idiom must relate to violence or attack. Another pitfall is choosing an option that sounds dramatic without carefully recalling the phrase in context. Reading editorials, opinion pieces, and non fiction can help you encounter idioms like this repeatedly and reinforce their proper meanings.

Final Answer:
"An axe to grind" means "to have a selfish interest", so option D is correct.