Researchers in the Wendlandt group at MIT are developing new selective, catalytic reactions. One example of a stereoselective reaction is the electrocyclic ring closure reaction. By name or number, identify each of the following electrocyclic ring-closing reactions that use a disrotatory stereochemical course: 1) Thermal ring closure of a six-pi electron system 2) Photochemical ring closure of a four-pi electron system 3) Photochemical ring closure of a six-pi electron system