The Ammonia and Methane in the Atmosphere of Jupiter Proved

The ammonia and methane in the atmosphere of Jupiter proved hard to detect because:

A) these molecules exist only in trace amounts in the atmosphere of Jupiter.
B) these molecules radiate mostly ultraviolet light, and this does not penetrate Earth's atmosphere.
C) these molecules radiate mostly long wavelengths, and these tend to scatter during the journey from Earth to Jupiter.
D) these molecules are unknown on Earth, so there spectra were not immediately recognized.