大全 145，sec05-09

                Astronomers at the Palomar
Observatory have discovered a distant supernova explosion, one that they
believe is a type previously unknown to science.

(A) that they
believe is

(B) that they
believe it to be

(C) they believe
that it is of

(D) they believe
that is（E）

(E) they believe
to be of

請問sc大全在哪裡下載呢? 謝謝你滴幫忙唷!^^

I think:

"that" is wordy and can be omitted because "one(a distant supernova explosion)" is objective.

that在这个地方是指 explosion.我们把explosion代回可以发现

they believe (explosion) is a type 错

they believe (explosion) it to be 错

they believe (explosion) that it is of 错

D中的that指代不清