The correct option is
D 's already seen / has already seen
The present perfect tense is used to describe something that happened in the past, but the exact time it happened is not important. It has a relationship with the present.
Have/has + past participle makes the present perfect.
In this sentence, a particular thing that has happened in the past has been described thus we would be using present perfect tense. Now since, the whole sentence is in the third person, we would be using "has" and not "have".
("have" is used in case of first and second person framed sentences.)
Now, for the past participle, it the form of a verb, typically ending in -ed in English, which is used in forming perfect and passive tenses and sometimes as an adjective. In this case the past becomes, "seen"
Option C is wrong as the mention has not been given in the bracket.
Option B is correct.