Question

Choose the correct alternative. Since around 1970, with World population of 3.5 billion, they have doubled it to our current level of over 7 billion in 2012.

• A. With world's population of 3.5 billion, doubling it.
• B. With world's population of 3.5 billion, doubling it.
• C. When the world's population was 3.5 billion, it has doubled it.
• D. When the world's population was 3.5 billion, they have doubled it.

Hint:

Use the past perfect tense to indicate that one past event occurred before another past event.

Answer 1

The Correct Option is C

To understand which alternative is correct, let's analyze the sentence structure and verb tense used. The question revolves around the description of the world population growth from 3.5 billion to over 7 billion, identifying the appropriate verb tense for past events and results significant over time.
The key phrases to consider in each option are:

• "With world's population of 3.5 billion, doubling it."
• "With world's population of 3.5 billion, doubling it."
• "When the world's population was 3.5 billion, it has doubled it."
• "When the world's population was 3.5 billion, they have doubled it."

The correct option is: When the world's population was 3.5 billion, it has doubled it.
This option uses the correct structure for conveying that when, in the past, the population was 3.5 billion, the process over time resulted in a doubling, reaching over 7 billion by 2012. The use of the past simple "was" together with the present perfect "has doubled" accurately reflects this growth timeline.