How are members to the House of Councilors elected?

a. Through a party list proportional representation method, based on a single nationwide district
b. Through a party list proportional representation method, based on districts at the prefecture level
c. Through a single nontransferable vote system, based on a single nationwide district
d. Through a single nontransferable vote system, based on districts at the prefecture level
e. Some by a party list proportional representation method based on a nationwide district and some from prefectures using a single nontransferable vote system

e