Correct Answer: C

Rationale: The correct plural of 'century' is 'centuries'. In English, to form the plural of most nouns ending in -y, you change the -y to -ies. Choice A, 'Centurys', is incorrect because it does not follow this rule. Choice B, 'Centures', is also incorrect as it does not provide the correct plural form. Choice D, 'Centuryies', is a completely incorrect and non-standard plural form of 'century'. Therefore, the correct answer is 'Centuries'.

Correct Answer: D

Rationale: The correct answer is D: At a Parent-Teacher meeting. A Parent-Teacher meeting is a formal setting where professional communication is expected. Using formal language in this context shows respect and professionalism. Choices A, B, and C involve informal or casual situations where using formal language may not be necessary or appropriate. Texting a friend, attending a family reunion, or Skyping with grandparents are typically more informal interactions where a more relaxed communication style is acceptable.

Correct Answer: C

Rationale: The correct plural of 'century' is 'centuries'. In English, to form the plural of most nouns ending in -y, you change the -y to -ies. Choice A, 'Centurys', is incorrect because it does not follow this rule. Choice B, 'Centures', is also incorrect as it does not provide the correct plural form. Choice D, 'Centuryies', is a completely incorrect and non-standard plural form of 'century'. Therefore, the correct answer is 'Centuries'.

Correct Answer: B

Rationale: The correct answer is B: 'The cat slept on the mat; she purred softly.' This sentence is a run-on because it contains two independent clauses ('The cat slept on the mat' and 'she purred softly') without proper punctuation. Choice A is incorrect as it is a compound sentence with a coordinating conjunction 'and' joining two independent clauses. Choice C is also incorrect as it is a compound sentence connected by a coordinating conjunction 'so.' Choice D is not a run-on sentence; it is a compound sentence with a coordinating conjunction 'or' joining two independent clauses.

Correct Answer: B

Rationale: The correct answer is 'I will be unable to come to your party.' This sentence uses formal language by avoiding contractions and employing a more polished wording. Choice A, 'I can't come to your party,' contains a contraction ('can't'), which makes it less formal. Choice C, 'I won't be able to go to your party,' though polite, still uses a contraction ('won't') and is not as formal as the correct answer. Choice D, 'I can't go to your party,' also includes a contraction and is less formal compared to the most formal choice, which is option B.