PSAs are often run free, and are to educate people about health, safety, or any other problem that affects public welfare.
A. for, mean
B. for, meant
C. of, to mean
D. in, meaning
网友回答
A. for, mean
(答案→)B. for, meant
C. of, to mean
D. in, meaning
解析：固定词组。For free免费；be meant to do sth 想要做某事；句意：PAS构成是免费的。想要教育人们关于健康，安全，或者其它一些影响公共福利的问题。