Ex.59 complete the text with could, couldn't, had to, didn't have to, didn't need to, needn't have, should have or shouldn't have and the verbs in brackets. not all are used in the text.

history contains a lot of stories about people who a (be) have been a little bit more careful. in 1576 the explorer sir martin frobisher sailed to the north of canada trying to find a way to asia. unfortunately, he b (find) it, but during the voyage, his men landed on baffin island as they c (look for) food and shelter. here he discovered some rocks which he thought contained gold. when he returned to england he showed the piece of rock to people who agreed that it was gold, and frobisher returned to the island with a larger ship. it was a difficult journey, as the ship d (avoid) huge icebergs. on the island there were polar bears which e (kill) a man quite easily and frobisher was worried that someone else would get to the gold first. perhaps he f (tell) so many people about his discovery, he thought. but he g (worry) about his secret. he found the place again, and his men h (work) in the freezing weather to dig for the gold. they returned to england again, and this time he i (stop) his discovery from becoming generally known. more and more people wanted to go to baffin island, and the next year the ships came back with hundreds of tonnes of gold. unfortunately, this is where things went wrong. when frobisher tried to sell the gold, he discovered that perhaps he j (show) it to more people in the first place. the people he had showed it to had been wrong. they k (tell) the difference between gold and iron pyrite, a compound of iron and sulphur. everyone laughed at sir martin and his men, and he l (admit) that he had made a mistake.