It is widely accepted that animals learn to do things because their certain acts lead to _______.

A．rewards

B．prize

C．awards

D．results

金钗石斛药材的特征是（）

A.呈长圆锥形，味微苦

B.茎圆柱形，嚼之有黏性

C.茎呈细长圆柱形，常盘绕成团，味淡

D.茎呈螺旋形或弹簧状，嚼之有黏性

E.茎扁圆柱形，表面有深纵沟，味苦