Recurring revenue is the portion of the revenue that is going to continue in the future. It provides a growing base of revenue on which management can rely while focusing on ways to grow the business.
on which,为什这里要加介词on？
介词on 跟rely 有关。由于rely 是不及物动词，没办法直接跟宾语，需要介词on 做中介，然后才能接宾语。所以，大家常说：rely on sth. ，这个sth. 就是关系代词which， 它是on 的宾语。这里是介词用在关系代词which 之前的一个例子。
“介词 + 关系代词”结构 解说：
“介词 + which” 就是把介词提到关系代词which 之前，它是定语从句中容易见到的语言现象，也是一些网友不容易学会的一个语法项目，问题的重点是这个“介词”较难确定。但它是有规律可循的，有以下几种状况，解析如下：
1. “介词+ which”可以替代关系副词when, where, why
替代when
Ill never forget the day on which my son was born.
我永远忘不了我儿子生的那一天。（on依据on the day确定）
The year in which the earthquake happened was 2008.
发生地震的那年是2008年。（in依据in the year确定）
替代where
This is the office in which I used to work.这就是我过去工作过的办公室。（in依据in the office确定）
He forgot the exact place in which he had hidden the jewelry.
他忘记了埋藏珠宝的确切地址。（in依据in the place确定）
替代why
Id like you to explain the reason for which you refused my offer.
我想叫你讲解一下你拒绝我的帮忙是什么原因。（for依据for the reason确定）
2. 依据与先行词搭配的具体意义确定用什么介词
Ill never forget the time during which I was with my friends in the country.
我从来不会忘记和朋友们一块在乡村度过的时光。
I will offer you a better way in which you can do the job.
我要给你提供一个做这项工作较好的方法。
3. 依据定语从句中动词或形容词的搭配来确定介词
She bought several clothes, on which she spent all her money.
她买了几件衣服，这类衣服花光了她所有些钱。（on依据spend…on确定）
It is the grammar rules of which I am not sure.
我没把握的就是语法规则。（of依据be sure of确定）
4. 依据定语从句所表达的具体意思来确定介词
Can you see the river across which there is a bridge?
你能看见上面有座桥的那条河？
He is swimming in the river, on which there is a boat.
他在那条河里游泳，河面上有一只小船。
Here is the river in which I used to swim.
这儿就是我过去常在里面游泳的那条河。
【注意】
有的“动词+介词”短语被视为一个固定的词组，不可分割。这个时候不可以把介词置于关系代词前，如：listen to, look at, look for, look after, care for, hear from, send for,等。
This is the right book for which Im looking.
This is the right book that Im looking for.
这就是我要找的书。
除此之外，除去“介词 + which”以外，假如定语从句的先行词是“人”，那样也可以用“介词+whom”引导定语从句，比如：Mary is the girl for whom I bought this gift. 玛丽就是那个我为其买此礼物的女生。