21.   This is an increasingly important source of revenue for many commercial organizations.

22.   Thus firewood is the most important source of energy in desert areas, where vegetation is sparse.

23.   Today they are an important source of food all over the world.

24.   ...an important source of foreign exchange.

25.   The air base was expected to be an important source of employment in the Crotone area, a depressed part of the Mezzogiorno.

26.   Thematic maps from satellite imagery represent an important source of data, particularly in third-world countries.

27.   Of these, the Sun is by far and away the most important source of energy.

28.   The clearing banks are important sources of short to medium term finance.

29.   Building societies are an important source of funds to residential developers.