Around 200 million people are employed in to...

Câu hỏi: Around 200 million people are employed in tourism worldwide, making it the largest industry in the modern global economy. It is estimated that three-quarters of a billion people go on holiday each year, and industry planners expect this figure to double (43) __________ 2020. Some of the biggest beneficiaries are less developed countries, where it is often their main source of income.

A. before

B. until

C. by

D. in