Tìm lỗi sai trong bài văn

Tìm lỗi sai trong bài văn sau :
(1) Professor Sanchez gave a lecture on transistors last Tuesday. (2) First, he explained what are transistors. (3) He said, that they are very small electronic devices used in telephones, automobiles, radios, and so on. (4) He further explained that transistors control the flow of electric current in electronic equipment. (5) He wanted to know which popular technological invention cannot operate without transistors. (6) Most students agreed, it is the personal computer. (7) Professor Sanchez then asked if the students know how do transistors function in computers. (8) He said that the transistors were etched into tiny silicon microchips and that these transistors increase computers' speed and data storage capacity. (9) Then he asked the class when had transistors been invented? (10) Sergei guessed that they were invented in 1947. (11) The professor said that he is correct. (12) Professor Sanchez then asked what was the importance of this invention? (13) Many students answered that it is the beginning of the information age. (14) At the end of the lecture, the professor assigned a paper on transistors. (15) He requested that each student chooses a topic by next Monday. (16) He suggested that the papers are typed. 

e.g: 1. True 
2. "what are transistors" → what transistors are were