Most scientists questions are based on?

I'm not quite sure as to what your question means, but here's an attempt to

1. Evolution (Who are our ancestors and how did we evolve), Universe (Are we really alone in the universe or are there extra-terrestrial life?), Medical (How do we beat bacteria?), amongst others.
 
2. If you meant as to what contextual (for the lack of a better word) devices they use (i.e. a textbook or the internet) then many scientists use a variety of things to start a hypothesis or their brains working. In this case, dreams can also help them. Many famous scientific discoveries were formed from way of the subconscious mind, like Mendeleev (who created the periodic table, or rather founded the idea of it.) There's also Alfred Russel Wallace (he discovered evolution based upon natural selection), Ellas Howes (who we all should thank because without him clothes wouldn't be sewn with a sewing machine...and might be a LOT more expensive then they are..) and we all know Einstein-Albert Einstein.

I hope that I was of help, if you need more clarification please don't hesitate to ask. 

The correct answer is c