I was playing basketball with Tom yesterday.强调我昨天“正在”与Tom打篮球
I played basketball with Tom yesterday.强调我昨天与Tom“打篮球”这件事情
二者侧重点不同,所以应该选择I was playing basketball yesterday.
你说的be动词用过去式再接动词应该是被动语态,应该用过去分词,例如：
He is loved by all his classmates.
所有的同学都喜欢他.
i+be+动词和i+动词造句有什么区别、.