单选题 以下代码输出的结果为: # include <stdio.h># include <vector>using namespace std;int main(){ vector<int> myv; vector<int>::iterator it; myv.push_back(1); it = myv.begin(); myv.insert(it,2); myv.push_back(3); it = myv.begin(); myv.insert(it,4); myv.erase(it); for(it=myv.begin();it!=myv.end();it++){ printf("%d",*it); }}