1. What is the definition of a prime minister according to the models of executive leadership?
A party leader chosen by members of Parliament based on their ability to maintain party unity.
Обяснение
The source explicitly states that a prime minister is 'a party leader chosen by members of Parliament based on their ability to maintain party unity within Parliament,' which is reflected in option two. The other options describe different roles or election processes not associated with the definition provided in the source.