Which sentence uses dashes correctly?

a.
on the last page of my program is„the lead dancer's autograph.

b.
now we will hike„along the ridge, down the hill, and across the creek.

c.
this sweater„the one that turned up at the bottom of my closet, does not fit me anymore.

d.
i want to hear everything, but„oh, someone is knocking on the door.