Fill in articles where necessary. (1) United Kingdom is situated on (2) British Isles which are separated from (3) continent by (4) English Channel and (5) Strait of Dover. (6) two main islands of (7) British Isles are (8)Great Britain and (9) Ireland. (10) England is situated in (11) south of (12) Great Britain and (13) Scotland in its (14) north. (15) two big islands are separated by (16) Irish Sea.

1. The

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8. a

9 an

11 the

12 the

15 the

1) The United Kingdom is situated on the British Isles which are separated from the continent by the English Channel and the Strait of Dover.

2) The two main islands of the British Isles are Great Britain and Ireland.

3) England is situated in the south of Great Britain and Scotland in its north.

4) The two big islands are separated by the Irish Sea.

Explanation:
1) The article "the" is not needed before "United Kingdom" because it is a proper noun denoting a specific country.
2) The article "the" is needed before "British Isles" because it refers to a specific group of islands.
3) The article "the" is needed before "continent" because it refers to a specific landmass.
4) The article "the" is needed before "English Channel" and "Strait of Dover" because they are specific bodies of water.
5) The article "the" is not needed before "two main islands" because it is implied that we are talking about the specific islands mentioned earlier in the sentence.
6) The article "Great" is needed before "Britain" because it is part of the official name.
7) The article "the" is needed before "Ireland" because it refers to a specific island.
8) The article "the" is not needed before "England" because it is a proper noun denoting a specific country.
9) The article "the" is needed before "south" and "north" because they refer to specific directions.
10) The article "the" is not needed before "Great Britain" in the second mention because it has already been established earlier in the sentence.
11) The article "the" is needed before "Scotland" because it refers to a specific country.
12) The article "the" is not needed before "Irish Sea" because it is a specific body of water.