在直角△ABC中,∠A=30°,∠C=90°,BC=2,则AB=______.
∵∠A=30°,∠C=90°,BC=2,
∴AB=2BC=2×2=4,
故答案为:4.
已知2A+3B = C+3D,又A和49 g B恰好完全反应,其生成57 g C和1 g D,,若B的相对分子质量为98,则A的相对分子质量为
A.16
B.27
C.44
D.56
Today the forests are getting fewer and fewer. We must down too many trees.
A.keep people from cutting
B.prevent people from cutting
C.stop people cutting
D.all the above