Explain why the futures price _t of a stock (without paying dividend) with

price _t satisfies _t = _t e^r(T-t) where r is the risk-free rate, and T is the maturing date. Can you use the same arguments to price all other types

of futures contracts? Furthermore, if the stock price _t follows a Geometric Brownian Motion, what is the process followed by the futures price _t Interpret your result.