You can't have one without the other, as the song says.就像歌里唱的那样，两者密不可分，不能只取其一。He had to have one leg amputated above the knee.他的一条腿不得不从膝部以上截断。Refusing to have one leader has not helped the cause.拒绝推举一名领导者对此项事业毫无帮助。...
聚羟基乙酸的经典制备方法主要有两种:直接缩合聚合法和乙交酯开环聚合法.There are two means available for the preparation of PGA - synthesis polymerization and ring - opening polymerization....