中国在本世纪国际竞争中立于不败之地的根本保证是( )
小明在教室里上课,但从校外的建筑工地上却传来施工的噪声,为了减弱噪声,以下方法可行的是( )
计算(﹣629)×45+2029×(﹣45)﹣15×1229.
It's very convenient ______ us to buy train tickets now because we can buy them either from the station or on the Internet.