Gullible and naive

[kulwant]

Test No. incompl/elem-10 "Present Tense", question 4

......... every single thing which that man says?

(a) Do you believe
(b) Is you believing
(c) Are you believing

Test No. incompl/elem-10 "Present Tense", answer 4

Do you believe every single thing which that man says?

Correct answer: (a) Do you believe
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can you explian me this question?

kulwant

[Torsten]

The speaker wants know if the other person gullible or naive or both.
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Test Of English for International Communication
TOEIC Preparation & TOEIC Vocabulary

[Snoopy_Blah_Blah]

Hello!
Could you, please, explain to me why we use which after every single thing in this sentence?
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Everything happens for a reason