问题如下：
Which of the following statements is correct regarding credit risk scoring models?
选项： A pooled model will result in scores
ranging from 300 to 850.
A custom model is cheaper to implement than credit bureau scores.
C.Multiple requests for new credit will reduce an applicant’s credit score.
D.An. example of a characteristic in a scoring model is the applicant's current gross salary of $50,000.
解释：
C An individual’s credit file will show a history of credit requests, with multiple requests causing an applicant’s credit score to decline. A credit bureau score model (rather than pooled model) will result in scores ranging from 300 to 850. A custom model is more expensive to implement than credit bureau scores. -Gross salary with current employer- is an example of a characteristic, with the actual salary number itself representing an attribute.
请问B里面的custom model是啥啊，为啥不便宜
