Read the excerpt from "mother tongue."

yet some of my friends tell me they understand 50 percent of what my mother says. some say they understand 80 to 90 percent. some say they understand none of it, as if she were speaking pure chinese. but to me, my mother’s english is perfectly clear, perfectly natural. it’s my mother tongue. her language, as i hear it, is vivid, direct, full of observation and imagery. that was the language that shape the way i saw things, expressed things, made sense of the world.

which best summarizes the central idea of the excerpt?

(a) nonstandard forms of english are valid, complete languages.
(b) people from different cultures can easily learn to speak english.
(c) the english and chinese languages have similar structures.
(d) parents should use standard english with their children in the home.