消防应急灯具的应急转换时间应不大于＿s。
A.15
B.5
C.2.5
D.0.25
参考答案：B
____ by taking part in practice can the young people be toughened and hardened into steel
A．Still
B．Just
C．Only
D．Yet
同时履行抗辩权在性质上属于（）.
A.法定权利
B.约定权利
C.延期抗辩权
D.永久抗辩权
