When factories and power plants in that area burned coal, fossil fuels, sulfur dioxide and nitrogen oxides
The characteristic is Temperature
The Great Wall of China was built to protect China from its enemies and invaders from the North, especially the Mongols (Mongols were a tribal group that would regularly conduct raids into China) the Great Wall of China was built in the 7th century BC and is located in Huairou District, China! Hope this helps
Toads eggs are normally near the water, attached to leaves or grass. They are normally in strands resembling black beads.
Frogs spread their eggs out on the water in clusters that are roundish. They look like a little clear glob with a black dot in them.