After people have learned that magnets attract things, centuries passed they took note of the fact that magnets sometimes also repel things.

A. what…that B. what…which C. what…how D. which…that

A. better than B. more than C. other than D. rather than

A. Long used B. Being used long C. Having been long used D. It has long been used

A. mustn’t have written B. couldn’t have written

C. needn’t have written D. might not as well have written

A. have worked B. have been working C. be working D. work on

A. for becoming B. to become C. of becoming D. becoming

A. Until B. Before C. Unless D. If only

A. as B. while C. after D. since

A. none but B. none other than C. nothing but D. no other than

A. needn’t have seen B. might have seen C. must have seen D. can’t have seen