19.For the past three months, I ____ hard for this exam.
A.worked
B.had worked
C.was working
D.have been working
出自:大学英语1

完成拼图验证

按住下方滑块,将拼图拖到缺口处后松开。

拼图背景,将小拼图拖到缺口处
向右拖动滑块