咳声如犬吠样,可见于()
A.百日咳
B.白喉
C.感冒
D.肺痨
E.肺痿
参考答案:B
—How often do you do sports? —I do sports______ /twaɪs/ a day.
A.twice
B.twins
C.tooth
D.tries
图示质量为m的物块,用两根弹性系数为k1和k2的弹簧连接,不计阻尼,当物体受到干扰力F=hsinωt的作用时,系统发生共振的受迫振动频率ω为:()
A.
B.
C.
D.