“$\tan x=\frac{\sqrt{3}}{3}$”是“$x=2k\pi +\frac{\pi }{6}\left(k\in Z\right)$”成立的（    ）

C

    Some children wish to be writers some day. They want to write stories or books for people to read. That's good! It's good to write something for people to read! But they should know that they need to be good readers first before they are really good writers. They should read a lot of books, instead(代替) of watching TV and spending a lot of time playing games when they are free.

    There is more fun in reading, and you want to look for more books to read.

    Before you decide(决定) to be a good writer, you'd better say to yourself, "I must read more and more!"