城市热岛效应出现的主要原因是 [ ]
A．纬度因素影响
B．地形因素影响
C．人类活动影响
D．海陆因素影响
答案：C
频率低于______HZ的声音叫做次声波，频率高于______HZ的声音叫做超声波，若这两种声波在水中的传播速度分别为V次和V超，则V次______V超（填“大于”/“小于”或“等于”）．
With their market share shrinking, analysts ______ that their profits have fallen by around 15%.
A．accomplish
B．reckon
C．promote
D．urge
