若某星球的密度与地球相同,它表面的重力加速度是地球表面重力加速度的4倍,则该星球的第一宇宙速度是地球第一宇宙速度的[ ]
A.1/4倍
B.4倍
C.16倍
D.64倍
答案:B
患者,男性,64岁,心前区疼痛4h,舌下含服硝酸甘油不缓解急诊入院。心电图示:V1~V5导联ST段抬高,弓背向上。实验室检查:血肌酸激酶同工酶增高。该患者的诊断为
A.不稳定型心绞痛B.急性心肌梗死C.主动脉夹层动脉瘤破裂D.心包炎E.病毒性心肌炎
Which statement about firefighting foam is TRUE?()
A.Foam conducts electricity
B.To be most effective,foam should be directed at the base of the fire
C.Foam is most effective on burning liquids which are flowing
D.Foam can ONLY be used to extinguish class A fires