已知某药物是按一级反应分解的,在25℃分解反应速率常数k=2.09×10-5h-1。该药物的起始浓度为94单位/cm3,若其浓度下降至45单位/cm3,就无临床价值,不能继续使用。问该药物的有效期当定为多长?
第1题
Could you find someone ________.
A) for me to play tennis with
B) for me to play tennis
C) play tennis with
D) playing tennis with
第2题
Are you interested ______ tennis?
A.in playing
B.for playing
C.on playing
D.to play
第3题
-- ______ do you play tennis? -- Twice a month.
A.When
B.What
C.How
D.How often
第4题
Are you interested ______ tennis?
A.in playing
B.for playing
C.on playing
D.to play
第5题
"Do you like to play tennis?" "Yes, I enjoy______ tennis.
A.playing
B.to play
C.play
D.the play
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