Most American colleges and universities use the grading system of A,B,C,D and F.
VOA : special.2009.03.05
This refers--this actually goes back to B.F. Skinner, a psychologist who flourished in the first half of this century.
这要追溯到B.F.斯金纳,一位活跃在上世纪前期的心理学家
金融市场课程节选 : 耶鲁公开课
So they began to call this A and this B and this C and this D and this E, this F, this G.
他们开始把这叫做A,B和C,这个是D,E,F,G
聆听音乐课程节选 : 耶鲁公开课
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