E
To play the E Chord, use the three fingers of your left hand as shown in the diagram, and strum all six strings.
In Exercise 15, when changing from an A chord to an E chord, the first finger slides lightly along the third string, back to the first fret, without being lifted off the string. The same sliding technique is used when changing between the D and E chords.
Rhythm Pattern
Rhythm Pattern
In Exercise 16, the first finger acts as a pivot finger between the A and D chords, and also as a slide finger between A and E. As this exercise has two chords per bar, you change chords half-way through the rhythm pattern.
In both of the chord progressions above, the first finger does not lose contact with the third string throughout the progression.