A.) Manufacturing plants :)
It can technically be a. since manufacturing plants are caused by humans since we were the ones who built and are currently using them. Automotive manufacturing plants are primarily facilitated for assembling vehicles with spot welds, and changes to high strength steel grades have had little effect on changing the industry’s joining preferences. However, while the basic technology used for spot welding is little changed, improvement in weld controls and process enhancements has extended the ability to successfully spot weld steel grades with higher carbon equivalents in high volume processes common in the industry. And the biggest release of greenhouse gases are burning fossil fuels which is what manufacturing plants do ALL the time.
It can’t be b. because volcanoes are formed by eruptions of lava and ash when magma rises through cracks or weak-spots in the Earth's crust. A build up of pressure in the earth is released, by things such as a plate movement which forces molten rock to exploded into the air causing a volcanic eruption. So humans can’t cause this naturally occurring event to happen.
It can’t be c. because the solar cycle affects activity on the surface of the Sun, such as sunspots which are caused by the Sun's magnetic fields. As the magnetic fields change, so does the amount of activity on the Sun's surface. One way to track the solar cycle is by counting the number of sunspots.
It can’t ALWAYS be d. Technically there is a possibility since most wildfires are caused by humans. Human-caused fires result from campfires left unattended, the burning of debris, equipment use and malfunctions, negligently discarded cigarettes, and intentional acts of arson. But sometimes, it can have the possibility of nature which a. doesn’t have because there have been wildfires due to lightning strikes.
So the best answer with most evidence to support it is a. manufacturing plants :)
