单项选择题
A．按键的同时单击鼠标左键即可
B．按键的同时单击鼠标右键即可
C．按住鼠标左键拖动鼠标，到达待格式化的文本末尾时松开鼠标键
D．按住鼠标右键拖动鼠标，到达待格式化的文本末尾时松开鼠标键
单项选择题 A （）system placed between the company network and the outside world may limit outside access to the internal network.
单项选择题 The Internet is an open system,and most information is available to everyone.It is very important to add（）to existing system for protecting the secret information.
单项选择题 C++ fully supports（）programming.