Which of the following gases were included under the Kyoto Protocol? (A)…

Concept: The Kyoto Protocol (1997), adopted under the UNFCCC, set legally binding emission-reduction targets for six greenhouse gases listed in its Annex A: carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6). The 2012 Doha Amendment later added nitrogen trifluoride (NF3) to this basket.

Application: Checking each gas named in the question against this Annex A basket — carbon dioxide, methane, and nitrous oxide are all directly listed there, so (A), (B) and (D) belong to the Kyoto basket. Nitrogen dioxide (NO2) and sulfur dioxide (SO2) are conventional air pollutants regulated under separate air-quality frameworks; neither ever appeared in the Kyoto Protocol's gas basket.

• Nitrogen dioxide (NO2) vs nitrous oxide (N2O): the two are easily confused by name, but NO2 is a criteria air pollutant, while only N2O (nitrous oxide) is one of the six original Kyoto gases.

• Sulfur dioxide (SO2) vs sulfur hexafluoride (SF6): SO2 is a conventional air pollutant; the sulfur-containing Kyoto gas is SF6, a chemically distinct compound.

Cross-check: Comparing against the standard list of the six original Kyoto gases (CO2, CH4, N2O, HFCs, PFCs, SF6) confirms that among the five gases named in the question, exactly carbon dioxide, methane, and nitrous oxide belong to the Kyoto basket — that is, only (A), (B) and (D).