and 连接两个不定式 谓语动词用单数还是复数?
如：To play basketball and to go swimming _____ useful for character-training.
A. is B. are
请详细说明解释，谢谢，急!!!!!!!!!!!!!!!!!!!!!!!!!
参考答案:B
用and连接的成分表单一概念时谓语动词用单数；就近原则；主语中含有某些连词(如as well as，besides，in addition to等)时，谓语动词的数同第一个主语保持一致。