下列视频分辨率格式，分辨率最低的是（）。
A.QCIF
B.CIF
C.4CIF
D.16CIF
参考答案：A
简述城市社会学研究的实践意义。
In the past few years, there _____ great changes in my hometown. [ ]
A. have been
B. were
C. has been
D. was
