直线y=2x+1经过点（0，a），则a=____ .
人体胚胎发育初期所需要的营养物质来自于（ ）
—In 1908 Lord Northcliffe offered a prize of ￡1,000 to the first man who would fly across the English Channel. Over a year passed before the first a____ was made.
下列说法不正确的是
