Read each sentence to find out whether there is any error in any part. Select the part that contains an error, or choose No error if the sentence is grammatically correct: That Brutus, who was his trusted friend had attacked on him caused heartbreak to Julius Caesar.

Introduction / Context:
This error detection question is based on a sentence about Julius Caesar and Brutus. It tests your understanding of verb and preposition combinations, especially in the phrase attacked on him. The sentence is intended to describe that Brutus, who was a trusted friend, attacked Caesar, and this betrayal broke Caesar s heart. You must find the part that is grammatically incorrect.

Given Data / Assumptions:
- Part a: That Brutus, who was his trusted friend.
- Part b: had attacked on him.
- Part c: caused heartbreak to Julius Caesar.
- Part d: No error.
- The structure describes a past action that deeply hurt Julius Caesar emotionally.

Concept / Approach:
The main grammatical issue lies in the use of the verb attack. In standard English, attack is a transitive verb that takes a direct object without a preposition. We say attacked him, not attacked on him. The presence of on after attacked is incorrect. The correct phrase should be had attacked him. The rest of the sentence, while slightly heavy, is grammatically acceptable in exam English and clearly expresses that this act of betrayal caused heartbreak. Therefore, the error is in part b.

Step-by-Step Solution:
Step 1: Read part a and confirm that That Brutus, who was his trusted friend is a correct relative clause giving background about Brutus.
Step 2: Examine part b and notice the phrase had attacked on him, where the preposition on seems unnecessary.
Step 3: Recall that attack is used directly with a person or object, so the correct form is had attacked him.
Step 4: Check part c and see that caused heartbreak to Julius Caesar is grammatically fine, so the only clear error is in part b.

Verification / Alternative check:
Rewrite the sentence correctly: That Brutus, who was his trusted friend, had attacked him caused heartbreak to Julius Caesar. For even better style, commas can be added for clarity, but the key grammatical correction is the removal of on. With this change, the sentence follows standard transitive verb usage. No other part of the sentence breaks basic rules of tense or agreement, so it is reasonable to identify part b as the sole error for exam purposes.

Why Other Options Are Wrong:
- Part a: correctly introduces Brutus and gives a relative clause who was his trusted friend; this structure is acceptable.
- Part c: caused heartbreak to Julius Caesar appropriately uses the verb caused with the noun heartbreak and the preposition to to mark the person affected.
- Part d and option e both suggesting no error are incorrect because the incorrect preposition on after attacked is a clear and standard grammatical mistake in exam level English.

Common Pitfalls:
Some learners become distracted by the overall complexity of the sentence and do not examine each verb phrase carefully. Others may feel that attack on is justified by analogy with similar sounding expressions. However, you should remember that many English verbs have fixed patterns and must be memorised. In practice, a quick test is to ask whether the verb normally appears with that preposition in reliable written sources. In the case of attack, the correct pattern is always attack someone or attack something without on.

Final Answer:
The error is in Part b; the phrase should be had attacked him, not had attacked on him.