为商业网点的形成和发展提供必要前提的因素是[ ]
A、交通条件
B、技术条件
C、自然环境
D、人口分布情况
答案：C
According to some scientists, the computer will do much harm to people''s health as smoking and drugs do.
A．does much harm ... smoking
B．will do as much harm ... cigarettes
C．will be doing as much harm ... smoking
D．does as much harm ... cigarettes
超声波是由波源振动而产生，其最低振动频率不小于
A．3000次/秒B．5000次/秒C．15000次/秒D．18000次/秒E．20000次/秒
