The correct option is
B the/a/the
Option (B) is the correct answer.
EXPLANATION:- There are two types of article.
DEFINITE ARTICLE(THE) :- Article "the" is used to refer to a DEFINITE person or thing.
INDEFINITE ARTICLE(A/AN) :- Article "a/an" is used to refer to a thing in general. For instance: man, door etc.
Article "a" is used with consonant sounds whereas article "an" is used with vowel sound.
In the first blank, article "the" will be used because "the" is used to refer to a particular/specific group of people.
In the second blank, article "a" will be used because the speaker is making a general statement.
In the third blank, article "the"will be used because article "the" is used to refer to a DEFINITE group of people like 'BRITISH PEOPLE'.