题干
All the students _______ very hard over the last three years.
A：works
B：has worked
C：have worked
D：worked
答案(点此获取答案解析）
C
All the students _______ very hard over the last three years.
A：works
B：has worked
C：have worked
D：worked
”是“函数
在区间
上为增函数”的（ ）
