Unwanted e-mail may ______

A．cause companies to fail in business

B．cause wanted e-mail messages to lose

C．damage the credit of a company

D．do good to a small company

分区配电网供电范围应清晰，不宜交叉和重叠，相邻分区间应（）

A、互相没有联络关系

B、互相重叠

C、联络越多越好

D、具备适当联络通道