Tourism accounted for close to 20% of the city’s economic output in 2015. 

【翻译】2015年，旅游业占了全市经济产出的近20%。

建议网友把 account for 作为一个固定词组记忆、理解即可，不要拆开分析了。

它有如下几种意思：

1. 对…负有责任；

2. 对…做出解释；

3. 说明……的原因；

4. 导致；

5. 占多大比例 （本句就是此意）

以下来自《词典》的详解，仔细体会：

1. PHRASAL VERB If a particular thing accounts for a part or proportion of something, that part or proportion consists of that thing, or is used or produced by it. (数量、比例上) 占...比例

例：

Computers account for 5% of the country's commercial electricity consumption.

电脑占了这个国家商业用电的5%。

2. 

PHRASAL VERB If something accounts for a particular fact or situation, it causes or explains it. 导致

例：

The gene they discovered today doesn't account for all those cases.

他们今天发现的那种基因解释不了所有的那些情况。

3. 

PHRASAL VERB If you can account for something, you can explain it or give the necessary information about it. 解释

例：

How do you account for the company's alarmingly high staff turnover?

你怎么解释这家公司高得惊人的人员流动率？

4. 

PHRASAL VERB If someone has to account for an action or policy, they are responsible for it, and may be required to explain it to other people or be punished if it fails. 对…负责

例：

The president and the president alone must account for his government's reforms.

该总统并且只有总统一个人必须对他的这些政府改革负责。