二次函数y=x2+2的顶点坐标是（ ）
下列唐朝与国外友好交往的史实，不发生在唐太宗时期的是( )
某地的年降水量是指（ ）
China began to open to the outside world in the late 1970s. _________, there have been great changes in the country.
