If you were asked to convert 25 cg to the unit hg, which of the following would be the first fraction used in the conversion?

You didn't like any choices. For what it's worth, I think this is a ridiculous question. There IS no right starting place. I think each person does it his/her way. I expect the answer your prof wants is to first convert from cg to g and the second factor to convert from g to hg.