Which of the following statements is true of dyslexia

A．It is a worldwide problem.

B．It is a regional problem.

C．It is a social problem.

D．It is a biological problem.

对话框在关闭之前，不能继续执行其他操作，这种对话框属于

A．输入对话框

B．输出对话框

C．模式(模态)对话框

D．无模式对话框