木杆上装设避雷线可直接用卡钉钉固，卡钉间距为（）mm。
参考答案：500
Which of the following statements regarding secondary markets is FALSE Secondary markets are important because they provide:（）
A. investors with continuous information.
B. firms with greater access to external capital.
C. regulators with information about market participants.
1999年至2004年期间，地质灾害造成的直接经济损失高于该期间年平均直接经济损失的年份有（）
A．1个
B．2个
C．3个
D．4个
