The New Instrument That Made It Possible for Edwin Hubble

The new instrument that made it possible for Edwin Hubble to demonstrate the existence of other galaxies in the early 1920's was:

A) the Hubble Space Telescope (that's why we named it after Hubble!)
B) the 300-ft radio telescope in West Virginia
C) a kind of electronic detector called a CCD
D) the 100-inch reflector on Mount Wilson
E) an infra-red telescope carried aboard one of the early airplane flights by the Wright Brothers
Section 26.2: Types of Galaxies