Как будет правильно? i used to swim in river или i used to swim in a river?

Первый вариант

Объяснение:

Артикль ставиться только с озёрами. Все остальное (река, море, пруд, океан и тд) идут без

used l to swim in a river

I.
When people (1) disagree with each other, they may have conflicts. Conflicts happen when people have different ideas or (2) values. It is not always possible to (3) prevent conflicts. But we can (4) resolve conflicts by (5) peaceful means means.

II.
They don’t get along with each other. 
It took him many years to get over the death of his parents.
I won’t be able to get away from the office before seven. 
I don’t want to put up with a society that supports smokers. 
What time did you get back last time? 

III.
provide - to offer (food, drink, etc.)
support - to help by approval, sympathy, or by giving money
discovery - finding or learning something
confident - a feeling that one can rely on oneself 
criticize - to indicate the faults of something

IV.
1. My freind said to watch this film.
2. Sasha said to tune in the radio at 7 o'clock the next day.
3. The doctor advised Nick to not eat fat food oane month.
4. The librarian said to Tanya to listen to that story on the radio.
5. My elder sister said to me to not go to that concert.

1. The Pacific is much larger than the Arctic or the Indian ocean.

2. Portugal is a small country in the west of Europe; on one of its borders is  Spain, on the other the Atlantic Ocean.

3. The Mont Blanc is the highest peak in the Alps.

4. The United Kingdom includes Great Britain and Northern Ireland; it

occupies the British Isles.

обьяснение:

артикль "the" ставится перед следующими названиями:

• страны, в названии которых присутствует элемент множественности: the United States  of America (группа штатов), the United Kingdom, the (former) Soviet Union, the Netherlands, the Philippines и др.

• страны, в названии которых присутствует слово "республика": the Dominican Republic, the Czech Republic.

• в названиях океанов, рек, морей, заливов и каналов: the Atlantic (Ocean), the Indian Ocean, the Mediterranean (Sea), the Black Sea, the (English) Channel (пролив Ла-Манш), the Amazon, the Dnieper River, the Suez Canal, the Persian Gulf.

• в названиях пустнынь: the Sahara (Desert), the Gobi (Desert).

• в названиях группы островов (элемент множественности): the Canaries, the Canary Islands, the Bahamas.

• в названиях горных гряд: the Rocky Mountains (the Rockies), the Smokies, The Carpathian Mountains, the Alps.

• в названиях частей света и регионов в следующих сочетаниях: the north (of Brazil), the south-east (of Spain), the north, the south, the Middle East, the Far East.

• в названии одного города: the Hague - Гаага.