possibly modal or d is not the actual root it just fits with the melody. try finding out wat notes are in the melody to find out wat key works best
A good guitar to start learning is a Yamaha or a Fender (the jap fenders) the American made are very expensive. There is also the Ibanez . You can use musiciansfriend.com or music123.com to find all kinds of guitars.
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The lead player is the one that plays what are called "riffs' . He uses scales basically all over the guitar. While the rhythm plays chords that accompany the guitar. When a performer plays the guitar he plays both. Or either one. If he stops singing and going to the guitar and starts making melody with it. he is playing lead. If he just stays strumming. He is just playing rhythm. Take the rolling stones for example the lead guitar player is Kieth Richards, there is another guy playing rhythm, and Mick Jagger only sings.