A)are an intermediate stage in the life of most stars. b) create immense amounts of radiation that are outside of the visible spectrum, so none have ever been observed by naked eye observations. c) are the result of exploding stars that initially are more than about eight times the sun's mass. d)explosions are relatively slow, typically taking about three to four million years.

C) are the result of exploding stars that initially are more than about eight times the sun's mass.

This is all you, but i can give you some topics that you could try. if it rained when you want to do something outdoors, it 'limits' that human activity. maybe you want to do an experiment that goes throughout the whole year and you have to have above freezing the entire year. this 'limits' your activity. i thought of those just off of the top of my head. something that gets to me that might be getting to you is you are thinking too hard about what to do. think simply, and if it is too simple, then bump it up just a little bit.

Answera discharge of static electricity;