Help with homwork - Astronomy
You will need to find out what population II 
 stars are.

When you understand what a population II star is, ask yourself two questions about each statement:

For example a) "Are population II stars out of the plane of the galaxy, and do they receive more cosmic rays", and "Would receiving more cosmic rays actually prevent life from forming". If you can answer yes to both questions, you have a potential answer.

If you judge that several answers are possible, then re-read the definition of a population II star, and ask which statement is most pertinent to the definition of such a star. Good luck.