中国的三叠纪，呈现出以（）为界，南（）北（）的地理格局。
参考答案：秦岭－大别山；海；陆
I wrote a letter to John for his help during my high school years，without which I ________ the college entrance exam.
A．would fail
B．would have failed
C．should fail
D．must have failed
中国环境标志的图形有什么含义？
