158. Every member of a certain club volunteers to contribute equally to the purchase of a $60 gift certificate. How many members does the club have? (1) Each member’s contribution is to be $4. (2) If 5 club members fail to contribute, the share of each contributing member will increase by $2. DS题答案是D,我怎么这题题目不理解,晕死。。。大家帮忙分析一下,感激不尽!!