Many people have been ill with a strange disease these days, _______ we’d never heard of before.

       A. one                          B. that    C. it                                 D. this

Many people have been ill with a strange disease these days, _______ we’d never heard of     before.

       A．one   B．that   C．it      D．this

Many people have been ill with a strange disease these days,____ we’d never heard of before.

A.one               B.that              C.it                    D.this