The effect of the medicine on this kind of disease remains .
A. seen
B. to be seen
C. seeing
D. to see
网友回答
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。