This question is incomplete, but I managed to find the rest of the sentence somewhere on the Internet.
So, the question is:
Whenever William is put in a tough or challenging situation, he seems to adapt fairly well. His easy-going nature, which is believed to be inherited from his mother, allows him to adjust to change quickly and effortlessly. William appears to have a well-established temperament.
The correct answer is temperament. Temperament is somebody's nature, character, personality, or just generally what a person is like and the way they behave when they are alone or surrounded by other people.