圆的面积S与半径R之间的关系式是S= πR2,其中自变量是( )。
R
—Sorry, the CDs you want have been sold out.
—How I wish I had bought ________ earlier![ ]
A. this
B. that
C. one
D. it
It's a good idea to get students to retell a story _____ their own words. [ ]
A. of
B. in
C. by
D. through