The correct answer is (b). T. Kajita is from Japan and A. McDonald is from the United States.
Takaaki Kajita is a Japanese particle physicist who shared the 2015 Nobel Prize in Physics with Arthur B. McDonald for their discovery of neutrino oscillations, which shows that neutrinos have mass. He is a professor at the University of Tokyo and a member of the Japan Academy.
Arthur Bruce McDonald is a Canadian physicist who shared the 2015 Nobel Prize in Physics with Takaaki Kajita for their discovery of neutrino oscillations. He is a professor emeritus at Queen’s University in Kingston, Ontario, and a member of the Royal Society of Canada.
The other options are incorrect. Option (a) is incorrect because T. Kajita is from Japan, not the United States. Option (c) is incorrect because A. McDonald is from the United States, not Canada. Option (d) is incorrect because both T. Kajita and A. McDonald are from Asia, not North America.