But becuase of our own problems with Iran, that has'nt happened.

这是不可能的。

普林斯顿公开课 - 国际座谈会课程节选

So you are supposed to know, for example, if x is t^, you're supposed to know dx/dt is nt^.

接下来你就会知道,例如,如果x=t^,那么dx/dt=nt^

耶鲁公开课 - 基础物理课程节选