A:合理利用水资源
B:保护和恢复天然植被、植树种草
C:设置沙障固沙
D:小流域综合治理
A. You can find our addresses from it.
B. You can find our information from it.
如图,直径为10的⊙A经过点C(0,5)和点O(0,0),点B是y轴右侧⊙A上一点,则cos∠OBC的值为( )