A:2,2-二甲基-3-丁烯
B:2,2-二甲基-2-丁烯
C:2,2-二甲基-1-丁烯
D:3,3-二甲基-1-丁烯
读等高线图,判断图中河流流向是( )
I have done everything possible to prevent him from running the risk but ______.