a
E|------------------------------------------------------|
B|------------------------------------------------------|
G|--------0------------0-----------0--------------------|
D|------4---4--------4---4-------4---4------------------|
A|---2--------2----2-------2---2-------2----------------|
E|-0-------------0-----------0--------------------------|

Then it changes to:
b
E|------------------------------------------------------|
B|------------------------------------------------------|
G|--------0------------0-----------0--------------------|
D|------4---4--------4---4-------4---4------------------|
A|---2--------2----2-------2---2-------2----------------|
E|-3-------------3-----------3--------------------------|
Like I said before, I'm not sure of the changes but it goes back and forth several times in the song

After playing through a and b several times switch to:
c
E|------------------------------------------------------|
B|-------0-----------0-----------0----------------------|
G|-----4---4-------4---4-------4---4--------------------|
D|---2-------2---2-------2---2-------2------------------|
A|-0-----------0-----------0----------------------------|
E|------------------------------------------------------|

d
E|------------------------------------------------------|
B|-------0-----------0-----------0----------------------|
G|-----4---4-------4---4-------4---4--------------------|
D|---2-------2---2-------2---2-------2------------------|
A|-3-----------3-----------3----------------------------|
E|------------------------------------------------------|
The song goes back to play a and b several times and back to c and d and back to a and b again.