As vitamins became recognized as essential food constituents necessary for health，it became tempting to suggest that every disease and condition for which there had been no previous effective treatment might be responsive to vitamin therapy.
(复合句：as从句，主句中的it是形式主语，不定式结构to suggest that…是真正的主语，that引导的宾语从句的主干是every disease and condition…might be responsive to vitamin therapy)
由于维生素被认为是健康必需的食物成分，所以过去无有效疗法的每种疾病和状况都可能会对维生素疗法起反应这一建议变得很有吸引力。
分句1：As vitamins became recognized as essential food constituents necessary for health
分句2：it became tempting to suggest
分句3：every disease and condition might be responsive to vitamin therapy.
分句4：for which there had been no previous effective treatment
3和4嵌套，4修饰3中的disease and condition
2和3嵌套，2和3构成宾语从句
1和2并列
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