What four-letter word can be written forward, backward, or upside down, and can still be read from left to right?

I’m not a test at school, But I have lots of choices. People use me to decide Who will speak with their voices.

It's nice to be important, But it's more important...

The hill where walking's dicey, or a book that's somewhat spicy.

Silent stage for dreams to play, where weary wanderers lay. With springs that hum a lullaby, beneath a sky of linen and cotton clouds, I cradle you softly until the sun returns.