Answer:
A). This would cause less frustration for teachers because they would not have to plan a lesson to reteach a concept that the students should already know.
Step-by-step explanation:
The option that most improves the conclusion, after being added post-sentence 3 is option A as it continues to describe the central idea of the passage more evidently by providing the benefits of year-round schooling. The other options are either opposing the claim of the passage or unable to present the central claim of the author. Only option A evidently supplies the author's idea and assists to develop a fruitful and effective conclusion. Thus, the correct answer is option A as it compliments the meaning of the passage.