I had been working on math for the whole afternoon and the numbers before my eyes.A. swim

问题补充：

I had been working on math for the whole afternoon and the numbers before my eyes.

A. swim

B. swam

C. swimming

D. had swum

答案：

A. swim

(答案→)B. swam

C. swimming

D. had swum

解析：句意：我一整个下午都在做数学题，那些数字在我的眼前转。主句用过去完成进行时，所以后半句用一般过去时，只有这样才能具备“过去的过去”的条件。选B。