My neighbors used to give me help ____ was always in time.用that行吗?

My neighbors used to give me help ____ was always in time.用that行吗?

用Which较准确.用that的话,可以改写为：
My neighbors used to give me help and that was always in time

不行，从句缺成份，应该用which

可以用THAT,而且只能用THAT，在定于从句中，that可以做主语也可以做宾语，而which只能做宾语，而在这里做主语