如果成千上万只昆虫生活在一株大树上，鸟以昆虫为食。那么树、昆虫和鸟的能量金字塔可表示为[ ]
A．
B．
C．
D．
答案：A
St. Louis has replaced Camden, New Jersey ______ the most dangerous US city, according to a study based on FBI crime data which was released Monday.
A．for
B．to
C．as
D．with
船舶处于“台风袭击中”航行，应该注意尽量避免转头，如果为形势所迫必须掉头，应慎重考虑（）并进行必要准备。
A．重心
B．浮心
C．稳心
D．漂心
