What I'm gonna do is draw a larger table, the same basic structure:

我要画个结构相同的大表格
I'm choosing Alpha and Beta on the rows,

用列来表示我选α还是β
my pair is choosing Alpha and Beta on the columns,

用行来表示我对手选α还是β
but now I'm going to put both grades in.

但我要把两人成绩写在一个单元格里
So the easy ones are on the diagonal:

这样就更直观了
you both get B- if we both choose Alpha;

如果我们都选α的话得B-
we both get B+ if we both choose Beta.

如果我们都选β的话得B+
But if I choose Alpha and my pair chooses Beta,

要是我选α我对手选β
I get an A and she gets a C.

我得A 她得C
And if I choose Beta and she chooses Alpha,

如果我选β她选α
then it's me who gets the C and it's her who gets the A.

我得C而她得A
So notice what I did here.

注意下我的表示方法