LEDs used in traffic lights are developed by Holonyak's students.

• A、 True
  
  

• B、False
  
  

• C、Not Given
  
  

According to the passage, which aspect of skyscrapers were some residents of North America concerned with in the late 1960's?

• A、The poor reception of radio and TV signals.
  
  

• B、The removal of trees and grass from building sites.
  
  

• C、The harmful effects on the city's plans.
  
  

• D、The obstruction of air traffic
  
  

Task 1

16.Paragraph     ①     

17.Paragraph     ②          

18.Paragraph     ③      

19.Paragraph     ④           

20.Paragraph      ⑤      

A.Education

B.Land and Climate

C.State System

D.General Introduction

E.Economy

F.Population