the <em>sun's corona</em> is only visable when there is a solar eclipse
D. Conclusion
After gathering data in support of a hypothesis, you can make a conclusion.
A hypothesis has to be tested multiple times by multiple researchers to become a theory. A fact has to be proven multiple times as well (but theory is a much better word).
B: between a nonmetal and a metal.
I think its C. global warming
because the other one directly threats aquatic bio diversity while global warming doesn't just affect aquatic biodiversity