In which year did the Kyoto Protocol, related to international control of greenhouse gas emissions, formally come into force?

Introduction / Context:
This question focuses on a factual detail about the Kyoto Protocol, one of the major international agreements on climate change. Knowing the year in which it came into force helps situate it correctly in the timeline of global environmental governance.

Given Data / Assumptions:

• The Kyoto Protocol is already assumed to be known as a treaty on greenhouse gas emission reduction.
• The options provide four consecutive years between 2004 and 2007.
• We must identify in which year the protocol actually entered into force, not when it was adopted.

Concept / Approach:
Many international treaties follow a two stage process. First they are adopted, and later they come into force after a certain number of key parties ratify them. The Kyoto Protocol was adopted in 1997, but only came into force years later after sufficient ratifications, including from major emitters.

Step-by-Step Solution:
Step 1: Recall that the Kyoto Protocol was adopted at the third Conference of the Parties to the climate convention in Kyoto in 1997.Step 2: It needed ratification by a required number of industrialised countries, representing a specific share of emissions, before it could come into force.Step 3: Russia's ratification was an important step that allowed the entry into force conditions to be met.Step 4: The protocol finally came into force on a specific date in February 2005.Step 5: Among the options, only 2005 matches this well known fact, so option B is correct.

Verification / Alternative check:
A quick mental check is to place Kyoto before the Copenhagen climate conference of 2009 and after the Rio Earth Summit era. Remembering that it was enforced in the mid 2000s, rather than the late 1990s, confirms 2005 as the correct year.

Why Other Options Are Wrong:
Option A, 2004, is slightly early and does not match the officially recognised date of entry into force.
Options C and D, 2006 and 2007, are too late and would push the implementation period beyond the commonly cited first commitment period of 2008 to 2012, which was based on the 2005 entry into force.

Common Pitfalls:
Students often confuse the year of adoption (1997) with the year of entry into force (2005). They may also misplace the protocol in the early 2000s timeline. Keeping in mind the difference between adoption and enforcement is crucial in such questions.

Final Answer:
The Kyoto Protocol formally came into force in the year 2005.