💡 Detailed Explanation
The correct choice is 'はず' (forming 'はずがありません' - there is no way / it is impossible that...). The grammar pattern '〜はずがない' expresses a strong subjective or objective conviction of impossibility based on logical evidence ('真面目な山田さん' - diligent Yamada). Sentence translation: 'There is no way that the diligent Mr. Yamada would break a promise.' 'つもり' (intention) and 'こと' (matter) do not form this strong negative conviction.