Bài 19 . Tìm các số nguyên tố thể viết được dưới dạng tổng các số nguyên dương liên tiếp bắt đầu từ số 2

a)56.16 + 17.243 (mod 16)

Exercise 4: Complete the sentences with one preposition in each gap.
1. Jordan bought a fantastic denim jacket for twenty euros, but he shopped.......... for hours before he
found it.
2. It wasn’t a good idea to buy those jeans without trying them ............. first – they’re too small!
3. I got this T-shirt for you. If you don’t like the colour, you can take it............ and change it for a different
one.
4. Dad’s buying lots of pairs of socks! Why? He’s stocking ........... on them, ready for winter!
5. We went to get some more of those cheap jeans but they’ve sold ............... so there were none left.
6. How long do you think it will take you to save ............ for those boots?
7. I’m going to have to choose between the shoes and the jeans – I haven’t got enough money to pay
............. them both!

Two men 1) were at sea in a small motor boat. It 2) _________ to rain and the sea 3) _________ very rough. Suddenly the engine 4) _________________. The men 5) _______ but they 6) __________ (not) start it again. Then a huge wave 7) ___________ against the boat and the two men 8) _________ into the cold sea. Luckily there 9) __________ a big ship nearby and the captain 10) __________ the two men. He immediately 11) ________ some of his crew to get a lifeboat and save the men. The crew in the lifeboat 12) ________ the two men and 13) _________ them onto their ship. One of the crew 14) ________ the men blankets and 15) _________ them hot drinks. When they 16) ________ at the harbour the two men 17) ___________ the captain of the ship and his crew for saving their lives.