识别并使用情态动词(如:Must 义务, Should 建议)。 Identify and use modal verbs (e.g., Must for obligation, Should for advice).
情态动词后的主动词必须是动词原形。 Main verb must always be in the base form after a modal verb.
构建肯定和否定句 (Cannot, Mustn't)。 Formulate positive and negative modal sentences.
对比 'Can's' 与其替代形式 'Be able to'。 Compare 'Can's' with its equivalent 'Be able to'.
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