股票交易可分为( )
A．现货交易
B．期货交易
C．期权交易
D．股票指数交易
E．贴现交易
参考答案：A,B,C,D
— Come on, Kitty.
— Oh, good heavens! Both my legs are nearly to give out. I ____ for hours like a dog. [ ]
A. have been walking
B. had walked
C. was walking
D. walked
观察学习的概念及特点是什么？
