19. The Hertzsprung-Russell diagram shown is divided into four sections.
Section 1
Hertzsprung-Russell Diagram
Section 2
10
......:
10*
Section 3
2
10
Luminosity (hun)
3
O
Section 4
ins
102
CLEAR ALL
104
400
200
45
30
100 75 55
Temperature (x10 K)
Which section of the diagram includes the coolest, brightest stars?