One of his greatest achievement was the discovery of the three laws of motion

Read the following passage and mark the letter A, B, C, or D to indicate the correct word or phrase that best fits each of the numbered blanks.

          Sir Isaac Newton, the English scientist and mathematician, was one of the most important figures of the 17th century scientific revolution. One of his greatest achievement was the discovery of the three laws of motion, (26) ______ are still used today. But he also had a very unusual personality. Some people would say he was actually insane.

          His father died before he was born, and his mother soon remarried. The young Isaac hated his stepfather so much that he once (27) _____ to burn his house down - when his stepfather and mother were still inside! Fortunately he did not, and he went on to graduate from Cambridge without being thrown into prison.

          Isaac's first published work was a theory of light and color. When another scientist wrote a paper criticizing this theory, Isaac flew into an uncontrollable rage. The scientist (28) ______ for the criticism was a man called Robert Hooke. He was head of the Royal Society, and one of the most respected scientists in the country. (29)_______, this made no difference to Isaac, who refused to speak to him for over a year.

The simple fact was that Isaac found it impossible to have a calm discussion with anyone. As soon as someone said something that he disagreed with, he would lose his temper. For this reason he lived a large part of his life isolated from (30) ______ scientists. It is unlikely that many of them complained.

(26)...................

• A. which
• B. who
• C. that
• D. they