The rivet the holds your planisphere (star& planet locator) together represents:
a. the north star : the brightest star in the sky

b. the north star: a second magnitude star

c. the hub of the universe

d. the nadir

e. nothing

correct option is B. The North Star: A second magnitude star

Explanation:

we know that different different star are at different different coordinates at different time of a year

and in the night sky we use planisphere to locate the star and this give us complete idea of location

and we know that in foreground there is a hole and by this we can see background and  location of star

and planimetric representation of the celestial sphere in Background of that instrument and we know at centre it is at polar and star is nearest to our north celestial pole

and this star is not the brightest star in the sky, it is 50th of all bright stars

so here correct option is B. The North Star: A second magnitude star