1、无疑
... it seems看来是 I am sure我可以肯定地说 to be sure无疑 ...
2、诚然
to be sure 诚然, 固然, 哎呀; 毫无疑问的; 肯定地，毫无疑问地……
3、当然
... title 5taItl n. 头衔,名称,标题; v. 赋予头衔 to be sure 毫无疑问；当然；必须承认；诚然 toil tCIl n.辛苦, 苦工, 网, 罗网, 圈套; v.苦干, 跋涉, 费力地做 ...
4、固然
...to be sure to do sth：必定会做某事；一定会做某事to be sure：诚然；固然；无可否认to be sure of yourself：自信；充满信心 ...