The Primary Mirror in the 10-M Keck Telescope Consists Of

The primary mirror in the 10-m Keck telescope consists of:

A) one large hollow honeycomb of glass-lightweight but relatively thick to prevent sagging.
B) one large, thin slab of glass whose surface is continuously adjusted by computer-controlled motors.
C) six individual mirrors, mounted so that they all bring the light to the same focus.
D) 36 individual mirrors, mounted so that they all bring the light to the same focus.