The people you find most diffcult      can also be your most valuable teachers.

A．dealing with

B．to be dealt with

C．to deal with

D．being dealt with

Windows 98虽然是一个比较成熟、健壮的操作系统，但有的也会出现应用程序在运行过程中“不响应”现象。用户如需强行结束一个应用程序，可通过按______组合键以打开“关闭程序”对话框。