如果四条线段m,n,x,y成比例,若m=2,n=8,y=20,则线段x的长是______.
∵m:n=2:8=1:4,
∴x:y=1:4,
∵y=20,
∴x=5.
Though winters in Britain are cold and there is usually snow, there are ________ places for skiing.
A.some
B.many
C.few
D.a few
请说说文献揭示的基本原则与方法。