In the chord diagram, the highlighted part represents the a) second finger

b) second string

c) third fret

d) open third string

It depends on what type of third separates the three notes.for example: if you have two mayor thirds is an "aumented chord"if you have two minor thirds is an "diminued chord"if you have one mayor first and then one minor is a "mayor chord"and inverted is a "minor chord"

Im not sure but i know it is not b

Do you have a link to the reading?  

1.    d. all of the above2.    c. increase the iso setting3.    true4.    true5.    false