it's是it is 的缩写,它里面有be动词is,it才是形式主语
it 英[ɪt] 美[ɪt]
pron. 它; 他; 正好是所需的; 事实[情况];
n. <美俚>傻瓜,笨蛋; <俚>绝妙的人; 理想的东西; 登峰造极;
[例句]He saw the grey Land-Rover down the bypass. It was more than a hundred yards from him
it's是it is 的缩写,它里面有be动词is,it才是形式主语