钢轨探伤车所用组合探头45°晶片的工作频率为()。
A. 3.5MHz
B. 2.25MHz
C. 1.25MHz
D. 1MHz
One of the serious weaknesses in American economy in the 1920s was()
A. uncontrolled speculation in the stock market
B. tariff protection
C. huge profits of big businesses
D. too much control over the banking system
对于共站址,由于HSPA+和LTE都会采用()技术,可以认为天线改造的成本相当;但对于LTE由于要弥补覆盖而增加站点需要新增天馈。