Here’s a possible way to fill in the blanks using the words provided:

English is the (1) **language** of the air. All pilots must speak English so that other pilots and air traffic controllers can understand them. English is also a very useful language (2) **for** passengers. All check-in clerks must speak English, and all announcements on planes (3) **are** given in English.

Today, when English is one of the major languages in the world, it's (4) **easy** to realize that this is a recent thing—that in Shakespeare's time, only a few (5) **million** people spoke English. English has become a world language because (6) **of** its establishment as a mother tongue outside England, in all the continents of the world. This exporting of English began in the seventeenth (7) **century** with the first settlements in North Africa. Above all, it is the great growth of population in the United States that has given the English (8) **millions** its present standing in the world.

People who (9) **speak** English fall into one of three groups: those who learned it as their mother tongue, those who have learned it as a second language, and those who are forced to use (10) **it** for professional or educational purposes.