问题
单项选择题
当一对相应啮合的渐开线齿轮的中心距做小量改变后，齿轮的瞬时传动比（）。
A.仍保持原值
B.发生变化
C.增大
D.减小
答案
参考答案：A
搜题请搜索小程序“爱下问搜题”
当一对相应啮合的渐开线齿轮的中心距做小量改变后，齿轮的瞬时传动比（）。
A.仍保持原值
B.发生变化
C.增大
D.减小
参考答案：A
| 完形填空。 | |||
| Marco Polo was a boy of about seventeen. Once, his father and uncle had just returned 1 their family in Venice after a long journey. They 2 about strange and beautiful lands in the East. They brought back gold and jewels. Shortly 3 . the Polo brothers asked him to 4 a trip with them to the East. So it was 5 Marco Polo’s journey (旅行) began. During three years of travelling to 6 China, he saw 7 that were almost unbelievable to a boy from Italy. He met people who had 8 ways of living. Some people 9 languages that he did not understand. At 10 they reached the continent of Asia. This was 11 the year 1257. The emperor made a great feast (盛宴) in honour of the Polos and asked Marco to live in his court. Marco Polo 12 to read, write and speak new languages. 13 the emperor sent him to 14 western and southern part of his empire. Marco Polo was given many soldiers and servants for his journey. Marco saw paper made by the Chinese. People in China had 15 discovered how to print 16 paper; they had many books and even used paper money! They burned little black rocks for 17 -later called coal. After three years, he wrote a book about his travels, 18 most people in Europe did not 19 . 20 many years later did the world know that this man had discovered a great eastern country. | |||
( )1.A. in | B. with B. thought B. before B. take B. when B. get to B. sights B. difficult B. said B. most B. of B. researched B. Since B. see B.Ssoon B. on B. heat B. what B. believe B. After | C. from | D. to |