现代OS具有并发性和共享性，是由（）的引入而导致的。
A.单道程序
B.磁盘
C.对象
D.多道程序
参考答案：D
The meeting was . Many people were for our plan. [ ]
A. success
B. a success
C. succeed
D. failure
被除数除以30，要想使商不变，除数也应除以30。[ ]
