Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the word(s) that best fits each of the numbered blanks from 43 to 47

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.

(44)______ , along with the economic benefits, this mass movement of people has resulted in environment. People often forget the damage caused by carbon emissions from aircraft, (45)______ contribute directly to global warming. Deforestation has cleared land in order to build hotels, airports and roads, and this has destroyed wildlife. In some areas, water shortages are now common because of the need to fill swimming pools and water golf courses for tourists. By pushing up prices for goods and services, tourism can also be harmful to people living in tourist destinations.

In response to these (46)______, some travel operators now offer environment-friendly holidays. Many of these aim to reduce the negative effects of tourism by (47)______ only hotels that have invested equipment to recycle waste and use energy and water efficiently. Increasingly, tourists are also being reminded to show respect for customs of the people whose countries they are going to visit, and to support local businesses, such as restaurants and shops which depend on tourism for their main income.

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. 

• A. 
  before
• B. 
  until
• C. 
  by
• D. 
  in