1. Introduction

Unit 7bc follows from Unit 7a, which means it expands the topic of security further. You will learn how to describe an incident, i.e. how to talk about simultaneous and consequent past events. In addition, you will find out how some of the security devices work. This means that you will learn how to explain technical principles using the Present Simple tense. In such situations, the Present Simple tense is necessary because a principle is something that does not change over time, but stays the same. Finally, you will have a chance to express your opinion on some security devices and pick the one that you think is the most useful and suitable for a particular purpose.

 

Contents:

Describing a technical principle using the Present Simple tense; using the Past Continuous tense to talk about simultaneous actions:

  • Each pulse generates a magnetic field in the coil.
  • While a passenger is walking through the walk-through metal detector, the alarm sounds if he has some metal objects.
  • While the passenger is walking through the walk-through detector, the official is studying a screen on a display unit.  

Talking about simultaneous past events using the Past Progressive/Continuous tense:

  • While a passenger was walking through the walk-through metal detector, the alarm sounded.
  • While the passenger was walking through the walk-through detector, the official was studying a screen on a display unit.