Since the difference in energy between the different rotational ...

[plus1]

Since the difference in energy between the different rotational states in a
molecule is very small, many molecular lines can be observed with:
A) visible light spectrometers.
B) radio or microwave telescopes.
C) high energy observatories like Chandra, in orbit above our atmosphere.
D) ultraviolet balloons flying above the ozone layer.
E) infrared telescopes on mountaintops.

[notis]

I know the answer! It's B.