What two things are needed to create an emission nebulae?
A) interstellar gas and dust
B) hydrogen fusion and helium ionization
C) cool stars and much interstellar dust
D) hot stars and interstellar gas, particularly hydrogen
E) hydrogen gas and carbon dust
Question 2
At which wavelength range is there no current or planned space observatory?
A) radio
B) infrared
C) visible
D) X-ray
E) gamma-ray