A：昼夜长短的变化
B：四季变化
C：极昼极夜现象
D：昼夜交替现象
Don't worry about him. ________he grows older，he will learn to deal with different problems properly.
一物体从高处自由下落，经2秒落地，则该物体下落1秒时，离地高度是（ ）
