How often does an el niño event occur?
a. about every other year
b. every 10 years
c. about every 2 to 3 years
d. about every 3 to 7 years

The correct answer is option D, about every 3 to 7 years

Reason -

El Nino comes at a regular interval of two to seven years. The last El Nino occurred in the year 2016 and it is forecasted that this year in 2019, the El Nino will come but its effect would not be as strong as that of year 2016. Also the El Nino in year 2019 will arrive late which shall means that the winters in 2019 will be a little warmer than the last year’s winter i.e 2018.

a fossil fuel is a fuel formed by natural processes, such as anaerobic decomposition of buried dead organisms, containing energy originating in ancient photosynthesis.[1] the age of the organisms and their resulting fossil fuels is typically millions of years, and sometimes exceeds 650 million years.[2] fossil fuels contain high percentages of carbon and include petroleum, coal, and natural gas.[3] other commonly used derivatives include kerosene and propane. fossil fuels range from volatile materials with low carbon to hydrogen ratios like methane, to liquids like petroleum, to nonvolatile materials composed of almost pure carbon, like anthracite coal. methane can be found in hydrocarbon fields either alone, associated with oil, or in the form of methane clathrates.

the theory that fossil fuels formed from the fossilized remains of dead plants by exposure to heat and pressure in the earth's crust over millions of years was first introduced by andreas libavius "in his 1597 alchemia [alchymia]" and later by mikhail lomonosov "as early as 1757 and certainly by 1763".[4] the first use of the term "fossil fuel" was by the german chemist caspar neumann, in english translation in 1759.[5]

in 2017 the world's primary energy sources consisted of petroleum (34%), coal (28%), natural gas (23%), amounting to an 85% share for fossil fuels in primary energy consumption in the world.[6] non-fossil sources in 2006 included nuclear (8.5%), hydroelectric (6.3%), and others (geothermal, solar, tidal, wind, wood, waste) amounting to 0.9%.[7] world energy consumption was growing at about 2.3% per year. in 2015 about 18% of worldwide consumption was from renewable sources.[8]