Rotational–vibrational spectroscopy is a branch of molecular spectroscopy concerned with infrared and Raman spectra of molecules in the gas phase. Transitions involving changes in both vibrational and rotational states can be abbreviated as rovibrational (or ro-vibrational) transitions.

Explanation:
The vibrational transitions of a molecule involve changes in the vibrational energy levels of the molecule. These transitions occur when the molecule absorbs or emits energy in the form of infrared radiation. However, vibrational transitions are not the only type of energy transitions that can occur in a molecule.

Rotational transitions, on the other hand, involve changes in the rotational energy levels of the molecule. These transitions occur when the molecule absorbs or emits energy in the form of microwave radiation. Rotational transitions are always accompanied by vibrational transitions because the energy levels of the two types of motion are coupled.

When a molecule undergoes a rotational transition, it also undergoes a vibrational transition because the two types of motion are coupled. This means that the energy levels of the two types of motion are not independent of each other. As a result, a molecule that undergoes a rotational transition will also undergo a vibrational transition.

In contrast, electronic transitions involve changes in the electronic energy levels of the molecule. These transitions occur when the molecule absorbs or emits energy in the form of visible or ultraviolet radiation. Electronic transitions are not always accompanied by vibrational or rotational transitions because the electronic energy levels of the molecule are not coupled to the vibrational or rotational energy levels.

Therefore, the correct answer is option B, that vibrational transitions are always accompanied by rotational transitions.