Many people have been ill from a strange disease these days we’ve never heard of before.A

问题补充：

Many people have been ill from a strange disease these days, we’ve never heard of before.

A. one

B. that

C. it

D. this

答案：

(答案→)A. one

B. that

C. it

D. this

解析：选A。one作同位语，指代前面的disease。