In need of a science geek:)?

Okay, no joke, I normally am a science geek. However, I've been sick and out of school for a while and my teacher expects me to do this mini lab. But, I don't have the proper material to do this at home (which she doesn't understand). So here is were I am asking a kind person like you to help me out on this:
 If you have ever made a circuit by using wire to link 2 light bulbs and one D-cell battery in a loop, what was the brightness of the bulbs like?
 If you have ever made a circuit by linking wire to 2 light bulbs and 2 D-cell batteries, what was the brightness of the bulbs like?
How do you figure out the voltage difference of each D-cell battery?

Thank you so much for helping me! If you answer this correctly, I will be happy to give you 'Best Answer' if you answered first. THANKS~:)