HTML5中doctype标签的正确定义是（）
<!DOCTYPE html PUBLIC "-//W3C//DTD// XHTML 1.0 Transitional//EN" "http://w3.org/TR/xhtml1-transitional.dtd">
<!DOCTYPE html PUBLIC "-//W3C//DTD// XHTML 1.0 Transitional//EN" "http://w3.org/TR/xhtml4/loose.dtd">
<!doctype html5>
<!doctype html>(正确答案)