The speed calculation is basically done as an average. Speed of an object at any point of time is called instantaneous velocity.
The average speed is the ratio of the total distance travelled over the total time consumed. Distance and direction, velocity and time, direction and velocity are wrong choices to measure the average speed.
Hence, the option (a), (b) and (c) are wrong
The average speed depends upon distance travelled and time taken. So, option (d) is the right answer.