——　Have you ever seen a whale alive?——　Yes I’ve seen ＿＿＿.A. that　　B. itC. such　　　D. one

问题补充：

——Have you ever seen a whale alive?

——Yes, I’ve seen ＿＿＿.

A. that

B. it

C. such

D. one

答案：

A. that

B. it

C. such

(答案→)D. one

解析：

one作为不定代词用来代替上文出现的单数可数名词；it为人称代词，指代前面出现过的某个事物；that常用来指代上文提到的不可数名词。