The effect of the medicine on this kind of disease remains .A. seenB. to be seenC. seeing

问题补充：

The effect of the medicine on this kind of disease remains .

A. seen

B. to be seen

C. seeing

D. to see

答案：

A. seen

(答案→)B. to be seen

C. seeing

D. to see

解析：句意：这种药对这种疾病的效果尚待观察。由题意可知，remain在此是用作系动词，且see这一动作还没有发生，答案锁定在B和D中间；“the effect”和“see”之间存在逻辑上的被动关系。