老师，我的一篇文章返修，讲的是一个血液学指标是疾病预后的危险因子。审稿人提的有一个意见是 The lack of validation for the main findings and conclusions.The authors have failed to devote any effort to validate their main findings with an independent cohort.我的这个研究的病例本来就很少，总共150例，很难能找到外单位的跟我合作做外部验证，请问该怎么回答审稿人的问题