采用互换装配时，选择的协调环不能为标准件或公共环。
参考答案：对
______ for some time after a tiring day is very enjoyable and exciting for me in summer.
A Swim B Swimming C Go swimming D To swim
刺激骨髓中红细胞再生的是
A．雌激素B．孕激素C．雄激素D．促卵泡素E．黄体生成素
