使冠状动脉血流量增多的因素是()。
A.主动脉舒张压降低
B.体循环外周阻力减小
C.心室舒张期延长
D.心室收缩期延长
E.心率增加
参考答案:C
The Space Shuttle Columbia broke into pieces over Texas as it returned to the earth on February 1,2003,__________all seven astronauts aboard.
A.having killed
B.killing
C.being killed
D.killed
2.1项危险品的名称是()。
A.易燃气体
B.杂项危险品
C.放射性物质
D.感染性物质