Let z be stochastic, and z(1) its value after a time period of length T. a) Identify two conditions under which the standard deviation of Z(T) is proportional to JT. b) Show that the standard deviation of Z(T) is proportional to VT under these two conditions. (Hint: You need to specify the unit of time, i.e. the measuring unit of T, and also the standard deviation of the change of a per unit of time.)