Modal verbs will often have synonymous meanings, depending on the sentence context. "Might" and "may" are prime examples. So unless a test sentence is very carefully phrased, there is a high liklihood of multiple correct answers. With that said, the following comments are respectfully submitted. Question: #1: Answer A also correct, and just as frequently used. #2: Answer B also correct #4: Answer B also. #5: Either answer. #9: Answer B also. Per the Oxford English Dictionary: " 'We could go' indicates a suggestion, possibility, or less certain ability to go somewhere." #12, #13: Answer A implies a pledge or promise. Answer B implies an obligation or liklihood. So either answer could be correct. #17: Answer A expresses a certainity. Answer B expresses liklihood or probability. #18: Both answers are totally synonymous in this context. So either. #20: Both imply a certainty of the loaning. Answer B is a somewhat more polite or subtle way of stating the point. #21: Answer A expresses a possibility. Answer B expresses a certainity. So either answer. #22: Both synonymous in this context. So either answer.