The correct option is A found
Option B: 'Found' is a verb that means 'discover after a deliberate search'. It relates to the given sentence, as the dog searched for the missing child and as a result, found him/her. Hence option B is correct.
Option A and D: 'Looks for' means the same as the above word, 'found'. But, the tense is in the present tense whereas the given sentence is in the past tense. The statement states an action that has already been completed "was given".
Similarly, 'seeks' is in the present tense.
Hence options A and D are incorrect.
Option C: 'Prevailed' means 'to prove more powerful or superior'. It does not complete the meaning of the sentence. Hence C is incorrect.