A red ball and a green ball are simultaneously thrown horizontally from the same height. The red ball has an initial speed of 40 meters per second, and the green ball has an initial speed of 20 meters per second. Compared to the time it takes the red ball to reach the ground, the time it takes the green ball to reach the ground will be:
[a] the same
[b] twice as much
[c] half as much
[d] four times as much