study的过去式是什么

His face was a study in concentration.

他脸上完全是一副全神贯注的表情。

This study represents a major expenditure of time and effort.

这项研究意味着要耗费大量的'时间和精力。

This study is the cornerstone of the whole research programme.

此项研究是整个研究计划的基础。

The first year provides students with a sound theoretical basis for later study.

第一年为学生以后的学习奠定坚实的理论基础。

The content of the course depends on what the students would like to study.

课程的内容取决于学生愿意学什么。