问题补充:
So far, several cases of a disease, as bird flu, are reported to have been found in the country.
A. knowing
B. to be known
C. having known
D. known
答案:
A. knowing
B. to be known
C. having known
(答案→)D. known
解析:考查非谓语。know 与cases为动宾关系所以用过去分词作定语。到目前为止据知是禽流感的几个病例在这个国家被发现并报道。