问题补充:
They to put their hearts into study..
A. have made their minds
B. have made their mind
C. have made up their minds
D. have made up their mind
答案:
A. have made their minds
B. have made their mind
(答案→)C. have made up their minds
D. have made up their mind
解析:考查短语固定搭配。本题考查短语固定搭配make up one’s mind下定决心做某事。mind的数随物主代词的数而变化。句意:他们已经下定决心投身于学习中。故C正确。