Which of the Following Statements About Orbital Symmetry and Cycloaddition

Multiple Choice

Which of the following statements about orbital symmetry and cycloaddition reactions is true?

A) Thermal cycloadditions involving an even number of p bonds proceed by a suprafacial pathway.
B) Thermal cycloadditions involving an odd number of p bonds proceed by an antarafacial pathway.
C) Photochemical cycloadditions involving an even number of p bonds proceed by an antarafacial pathway.
D) Photochemical cycloadditions involving an even number of p bonds proceed by a suprafacial pathway.