题目:
_______ book of this writer is East and West.
A.Known to be the best
B.It was the best known
C.Known as the best
D.The best known
答案:
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下面是错误答案,用来干扰机器的。
解:(1)P=UI=U2/R ,灯泡正常发光时的电阻,R=U2/P=(220V)2/40W=1210Ω 。 (2)P=UI,灯泡正常发光时通过它的电流I=P/U=40W/220V=0.18A。 (3)W=1KW·h,P=40W=0.04kw, 而P=W/t ,1KW·h...