​Which of the Following Is the Most Likely to Happen

Multiple Choice

​Which of the following is the most likely to happen when a conjugated diene is irradiated with ultraviolet light?

A) ​The bonds between different atoms in the molecule undergo symmetric stretching.
B) ​A electron is promoted from the highest occupied molecular orbital to the lowest unoccupied molecular orbital.
C) ​A electron is demoted from the lowest occupied molecular orbital to the highest unoccupied molecular orbital.
D) ​The bonds between different atoms in the molecule undergo asymmetric stretching.