PSAs are often run _____ free, and are ______ to educate people about health, safety, or any other problem that affects public welfare.A.for, meanB.for, meantC.of, to meanD.in, meaning
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B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。