The key answer of exercise 4

a)

• Past Simple → announced, lived, used, could find, isolated, didn't speak, arrived, allowed
• Past Continuous → was working
• Past Perfect Simple → had found, had existed
• Past Perfect Continuous → had been living

b)

1. 1a) means Elizalde had left the country before the truth came out.; 1b) means Elizalde was in the country at the time the truth came out, and then he left immediately. Here 1a) is more appropriate; the truth came out after Elizalde had left the country.
2. 2a) uses the continuous to emphasise duration (the long period of time).; 2b) is also possible but doesn't emphasise duration as strongly as 2a).
3. 3a) and 3b) are similar in meaning.

c)

1. chronological
2. progress
3. before
4. length