他接受了一系列医学检查，但医生没有发现任何问题。

He underwent a ___series of medical tests, but the doctors could not find anything wrong.

去年她就现代美国小说家发表了一系列引人入胜的讲座。

She delivered a fascinating ___series of lectures last year on modern American novelists.

本报告旨在为改进培训计划提出一系列实用的建议。

This report aims to make a ___series of practical suggestions for improving the training program.