【正确答案】 A

【答案解析】这是一个涉及惯用法的试题。in turn有两个意思：(1)“轮流”，(2)“反过来”。如：We looked after the children in turn. “我们轮流照看孩子。”Theory is based on practice and in turn serves practice. “理论基于实践，并反过来为实践服务。”in return“报答，回报”，通常后面与介词for连用。如：I wish I could do something in return for your kindness. “但愿我能做些什么以报答你的好意。”by chance“偶然地”，如：I came across this old photo in the drawer by chance. “我偶然在抽屉里看到了这张旧照片。”by turns“轮流，交替”，如：She laughed and cried by turns. “她一会儿笑一会儿哭。”按照本句意思，只有in turn合适。