I had been working on math for the whole afternoon and the numbersbefore my eyes.A. swimB.

问题补充：

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

A. swim

B. swum

C. swam

D. had swum

答案：

A. swim

B. swum

(答案→)C. swam

D. had swum

解析：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。句意：我一整个下午都在做数学题，那些数字在我的眼前晕眩。

【考点定位】考查动词时态。