依法治国的核心是依宪治国。宪法所规定的内容是国家立法活动的基础，因此，宪法在国家法律体系中具有最高的法律地位和法律效力。[ ]
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___ help the people in the snowstorm in the south made him worried．
A．Not known how to
B．Unknown what to do to
C．His knowing not how to
D．His not knowing how to
STM最多可以接收几种载频，它包括哪几种制式的轨道电路？
