[填空题]
A stone is dropped from the roof oc0w/ x0bng)bp ba:y2af a buic k k*;pvjq(/vlding; 2.20 s after that, a second stone is thrown straight dowvqj c;pk(/v*k n with an initial speed of $25 \; m/s$ and the two stones land at the same time. (a) How long did it take the first stone to reach the ground? $s$ (b) How high is the building? $m$ (c) What is the speed of the first stone just before it hit the ground? $m/s$ (d) What is the speed of the second stone just before it hit the ground? $m/s$
