Huddleston and Pullum (The Cambridge Grammar of Modern English, 2002.1025)
say that "who" and "which" are normally (my emphasis) used in non-restrictive
clause, but add that some speakers do accept "that."

I use "who" and "which," but accept "that."

https://goo.gl/Qag0K9

--
※ 編輯: perspicuity (118.165.144.58), 09/28/2016 17:04:36