20. In many developing countries, rural-to-urban _____ is another cause of the increasing rate of child labor. (A) isolation (B) interrogation (C) migration (D) persuasion (E) integration II. Grammar and Structure. 20 points A. Please choose the best answer to complete the sentence. 【單選題】每題 1 分，共 20 題，答錯 1 題倒扣 0.25 分，倒扣至本大題零分為止，未作答，不給分亦不扣分。