56. Which of the following mechanism changes the constant speed rotary motion into intermittent reciprocating linear motion？ (A)Chain drive (B)Cam mechanism (C)Simple gear train (D)Worm and wheel

59. Which of the following statements about the structure is incorrect？ (A)The arch structure is well stressed, the disadvantage is that it takes up space. (B)The truss structure uses simple materials to withstand weight, and is often used to build bridges. (C)The cable structure is cheap and beautiful, and it is often used as the main structure of the building. (D)The beam-column structure is very stable for building houses, but it takes up space and consumes materials.

56. Which of the following mechanism changes the constant speed rotary motion into intermittent reciprocating linear motion？
(A)Chain drive
(B)Cam mechanism
(C)Simple gear train
(D)Worm and wheel

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