单选题 They ______ to his birthday party this evening if they have something important to do.

【正确答案】 D
【答案解析】[解析] 考查情态动词。need既可作情态动词，也可作实意动词，作情态动词时可以直接加not否定；作实意动词时，在前面加助动词否定，且后跟不定式时，须加不定式符号to，即don't need to do。故选择[D]。