In the following questions, few sentences are given. Choose and mark the sentence which contains no grammatical or contextual error in it. If all the sentences are grammatically and contextually incorrect, mark "All are incorrect" option as the answer choice.

The correct answer is "He admitted to forging the signature on the lease agreement knowingly."

Detailed Explanation and Grammatical Analysis:

Let's analyze each given option step-by-step to identify why four of them contain grammatical errors and why the third sentence is completely correct:

1. "She would rather to forfeit her claim than drag the dispute into litigation."
• Error: Use of full infinitive ("to forfeit") after "would rather".
• Rule: The expression "would rather" is followed by a bare infinitive (infinitive without "to").
• Correction: "She would rather forfeit her claim than drag the dispute into litigation."

2. "The magistrate along with his clerks were seated when the hearing resumed."
• Error: Subject-Verb Agreement error.
• Rule: When two subjects are connected by phrases like "along with", "together with", "as well as", or "accompanied by", the verb agrees with the primary (first) subject. Here, the subject is singular ("The magistrate"). Therefore, the verb must also be singular ("was" instead of "were").
• Correction: "The magistrate along with his clerks was seated when the hearing resumed."

3. "He admitted to forging the signature on the lease agreement knowingly."
• Analysis: The verb "admit to" is correctly followed by a gerund ("forging"). The prepositions, noun usages, and sentence structure are grammatically and contextually correct without any errors.

4. "Every one of the cadets are obligated to report at dawn for physical training."
• Error: Subject-Verb Agreement error.
• Rule: Phrases beginning with "Every one of..." take a singular verb because the subject is "Every one", which refers to each individual unit singularly.
• Correction: "Every one of the cadets is obligated to report at dawn for physical training."

Therefore, the sentence containing no grammatical or contextual error is: "He admitted to forging the signature on the lease agreement knowingly."