I have a feeling that George will be leaving the company soon, because the boss's secretary told me.

We can't use the article "a" with the word "pants"; we have to say either "a pair of pants" or use the word "pants" (usually with another modifier — "My pants are ripped."). You might hear "a pant" (in reference to a single pair of pants) in some American clothing advertisements, but that's a silly affectation.

What a pleasure to hear from Nepal, the 120th country in our list of countries heard from! (Other recent additions are Senegal and Aruba.)

Authority: The New Fowler's Modern English Usage edited by R.W. Burchfield. Clarendon Press: Oxford, England. 1996. Used with the permission of Oxford University Press.

Thanks in advance for your help!

Two other suggestions are made: Great Britain had ruled North America for more than a century when the Independence War broke. Great Britain had been ruling North America for more than a century when the independence War broke. Thanks a lot for your answer.

1. At the end of the last century, Great Britain had ruled North America for twenty years.
2. At the end of the last century, Great Britain had been ruling North America for twenty years.

1. The phrase "for twenty years" indicates a stretch of past time that ended with "the end of the last century," so there are, in fact two past times being contrasted: the fixed past time (end of the century) and the earlier 20 years. Therefore past perfect is necessary.
2. The choice between simple past perfect and past perfect progressive is more about drama than about completion. Both choices are possible here. Simple past perfect is more factual: Britain had ruled for 20 years, and that's just the way it was. Past perfect progressive is more intense and literally progressive: Britain had been ruling for 20 years and it felt like a long time, a lot had happened, the whole period had a sense of action or progression.
3. If you want to imply that Britain's rule was about to end and fall away into history, then the simple past perfect sets the scene into that more objective framework. But if you want to imply that Britain's rule was still in full power and likely to continue for a few more important years, then the past perfect progressive sets the scene into that more impassioned or action-filled framework. But to assert clearly that Britain's rule was completed by the end of the century, you'd have to add another sentence or phrase—the simple past perfect by itself wouldn't do it.
4. The clause in the alternate version "When the independence war broke" is the same as "at the end of the last century": it simply establishes a fixed past moment before which the other action took place. So the same principles apply.