问题
选择题
It's always difficult being in a foreign country, _____ when you can't speak the language. [ ]
A. extremely
B. naturally
C. basically
D. especially
答案
答案：D
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It's always difficult being in a foreign country, _____ when you can't speak the language. [ ]
A. extremely
B. naturally
C. basically
D. especially
答案：D
其中L是圆柱面x2+y2=2y与平面y=z-1的交线，从x轴正向看去取逆时针方向．