一根弹簧在弹性限度内,对其施加30N的拉力时,其长为20cm,对其施30N压力时,其长为14cm,则该弹簧自然长度为()cm,其劲度系数为()N/m。
参考答案:
17;1000
生后第一年身长一般可增加()
A.15cm
B.20cm
C.25cm
D.28cm
E.30cm
According to the passage, which of the following offers most of the HDTV programmes so far
A.Retailer delivery services.
B.Cable providers.
C.Commercial television stations.
D.HDTV set manufacturers.