要保证一个公司总部与其分支机构的网络通讯安全只有通过VPN来实现
参考答案：错
典型的不可抗力事件是：（）
A.未预计的工作负担
B.严重的疾病
C.特别差的天气
D.由于分包商的疏忽而导致的拖延
They haven't finished their work. Maybe they have some trouble ______ it. [ ]
A. on
B. at
C. in
D. with
