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:

Tense consistency is vital. Use “was” for past reference and present perfect (“has doubled”) for continuing relevance.

Answer 1

The Correct Option is C

The clause refers to a past event (“1970”) → use past tense “was”.
"Has doubled" connects to the result seen “in 2012”.
So, “When the population was 3.5 billion, it has doubled it” captures both the reference point and the action.
Though this sentence is not perfect, among the given options, (C) is structurally most correct.