too busy to do sth 太忙以至于不能做.
按这个短语搭配及其意思, A和B都不对.
A they were too busy to walk with each other,句子已经完整了,后面the time不好加了
B they were too busy talkingg with each other to forget the time, 语法上没有问题, 但是语义上不合逻辑.他们都忙于互相交谈而不能忘记了时间.要是改成 to remember可以