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!!!!!!!!!!!!!!!!!!!!!!!!!

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。