二次函数y=ax²+bx+c（a≠0）的图象如图所示，下列结论：①b＜0；②c＞0；③a+c＜b；④b²﹣4ac＞0，其中正确的个数是（   ）

俄罗斯完全在亚洲部分的工业区是（    )

    A long time ago，there was a craftsman．His name was Lu Ban. One day，he was at work on a mountain．A leaf cut his finger．He saw many sharp teeth on the leaf．"Could I make a____with teeth like these? I could cut things with it ____，"he said to____．Soon he made a saw. It was the first____in the world．People are____using this tool today．

关于万有引力定律，下列说法正确的是（   ）