The most serious environmental damage that may result from our use of fossil fuels is

Of the many environmental and public health risks associated with burning fossil fuels, the most serious in terms of its universal and potentially irreversible consequences is global warming. In 2014, approximately 78 percent of US global warming emissions were energy-related emissions of carbon dioxide.

Explanation:

a tetrad is the foursome during meiosis made by two homologous chromosomes that have each already replicated into a pair of sister chromatids.

the second type of galaxy is called a barred spiral, which has a thing called a bar straddling the nucleus