The correct answer is 'gullible.' Key Points - In the given sentence, we need a word close to the meaning of 'trustful' to fill in the blank. - Let us see the meanings of the given words: - Fallible: capable of making mistakes or being wrong. - Gullible: easily persuaded to believe something; credulous, trustful. - Sensible: done or chosen in accordance with wisdom or prudence; likely to be of benefit. - Credible: able to be believed; convincing. - From the meanings of the words, we can say that 'gullible' is the most appropriate answer. -Therefore, the correct answer is 'gullible.' The correct sentence: My son is very gullible, he trusts everyone.