study的過去式是什么

　　His face was a study in concentration.

　　他臉上完全是一副全神貫注的表情。

　　This study represents a major expenditure of time and effort.

　　這項研究意味著要耗費大量的時間和精力。

　　This study is the cornerstone of the whole research programme.

　　此項研究是整個研究計劃的基礎。

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

　　第一年為學生以后的學習奠定堅實的理論基礎。

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

　　課程的內容取決于學生愿意學什么。