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。