Choose from the list below appropriate reasons why the Diels-Alder reaction is synthetically useful. Check all that apply.
a) It allows for the formation of multiple bonds in a single step.
b) It is highly selective, often producing only one regioisomer and one stereoisomer.
c) It can be used to synthesize complex ring structures efficiently.
d) It can incorporate a wide range of functional groups.
e) It requires harsh reaction conditions, making it applicable to a variety of substrates.
f) It is a reversible reaction, facilitating equilibrium control during synthesis.
