"dog hidden" vs. "dog hid"

[Lens]

English Grammar Tests, Elementary Level

ESL/EFL Test #83 "Past Participle Sentences", question 8

After looking for him all day, Jeremy finally found his dog ......... under a cave.

(a) hid
(b) hide
(c) hidden
(d) hit

English Grammar Tests, Elementary Level

ESL/EFL Test #83 "Past Participle Sentences", answer 8

After looking for him all day, Jeremy finally found his dog hidden under a cave.

Correct answer: (c) hidden

Your answer was: incorrect
After looking for him all day, Jeremy finally found his dog hid under a cave.
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Why we use "hidden"?

Lens

[Mister Micawber]

.
Only the hidden form of the past participle is commonly used as a modifier.
.
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Canadian-American native speaker
who teaches English for a living at Mister Micawber's
ESL cafe: Interview with Mr. Micawber