那是当然用英语可以说成 "of course"。这个说法来源于英语表达 "of course" 意为 "显然，无疑地"。例句：

"Do you want to go for a walk?" "Of course, I could use some fresh air." (你想去散步吗？当然了，我需要点新鲜空气。)

"Do you think she'll agree to help us?" "Of course, she's always been very helpful." (你觉得她会同意帮助我们吗？当然了，她一直都很乐于助人。)

希望这些例句能帮助你理解 "of course" 的用法。