An index fossil is a fossil that is useful for dating and correlating the strata in which it is found.
Or it is a fossil that helps you find the date where it has been found. I rephrased that.
Because if you have a liquid then you need a glass to keep it together and when it is a solid it is already together so you don't need to do anything
The answer is B, Let me know if you get it right!
Heat can be absorbed or produced