带有五棱镜的反光照相机,其影像与物象上下左右完全一致。()
参考答案:对
女性,26岁。感冒后第5天出现心悸、气促、心率120次/分,心尖区第一心音减弱,有奔马律,有心尖区收缩期吹风样杂音Ⅱ级。对确诊最有意义的检查是()
A.心电图
B.胸片
C.血沉
D.血清病毒中和抗体
E.超声心动图
In order to get names of schoolboys(SEX='M')whose age=22, from a relation S(SNO,SNAME,SEX,AGE),which of the following expressions is (are) correct Ⅰ.πsname(σsex='M'^age=22(S)) Ⅱ.σsex='M'^age=22(πsname(S))
A. Ⅰ only
B. Ⅱ only
C. Ⅰand Ⅱ
D. neither