Value-added services have become the major income source of telecommunication operators.

增值电信服务已经成为电信运营商的重要收入来源。

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Tourism is a major source of income for the area.

旅游业是这个地区的主要收入来源。

《牛津词典》

For example, tourism is the major source of income in Bermuda, Greece, Italy, Spain, Switzerland and most Caribbean countries.

例如，旅游业是百慕大、希腊、意大利、西班牙、瑞士和大多数加勒比国家的主要收入来源。

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The United Nations Security Council later imposed sanctions on Pyongyang, which have impeded its efforts to sell conventional weapons abroad, a major source of income for the cash-strapped nation.

VOA: standard.2009.12.08

The new Medicare reimbursement coincided with urologists' loss of a major source of income.

WSJ: Medicare Investigation Reveals a Sharp Rise in Controversial and Expensive Prostate Cancer Treatment

Scam emails and infected websites still represent a major source of income for cyber criminals.

CNN: Why cyber attacks threaten our freedom

And yet, logging represents a major source of income for Cambodia's cash-strapped government.

CNN: ASIANOW - TIME Asia | 'There Was Method to My Madness'