Когда пишется артикаль an, а когда a ?

lt/rain often in winter?

1. Many years ago _ rivers began to speak against _ sea. _ rivers came to _ sea and said "We bring _ sweet water to you, and you make it salt. _ people can't drink this _ water. Why do you do that?" "If you do not like _ salt water", answered _ sea, "run to _ some other place".
2. Once _ two friends were in _ thick wood, when they met _ bear. One of _ men was very much frightened by _ bear. He ran to _ high tree and got up into it. _ other man understood that he could not stand up against _ big bear. He lay down on _ grass. "_ bear will think that I am dead", he said to _ himself. _ man thought that _ bears do not atack _ dead people. _ bear came up to _ man on grass, sniffed at _ his nose and went away. _ other man got down from _ tree. "What did _ bear say in _ your ear?" he asked him. "He told me", was _ answer, "not to go into _ woods with _ bad friend who will not help you in _ danger."
3. _ man built _ house for _ himself. _ house was nice, but very small. He invited _ friends to see it. _ friends came and looked at _ house. Every man said something bad about it. "_ front of _ house is not nice." "_ windows are very small." "_ roof is not good, _ rain will come in." "_ rooms are not large enough for _ man." _ man listened and answered, "You may be right. _ house is small, but it is big enough for _ me and I have no _ good friends to invite to _ my house."

official name of the whole country? 4.When was the name "United Kingdom " first used? 5.What do people also call the United Kingdom of Great Britain and Northern Ireland ?