25 !
(lc)which sentence below shows correct use of em dashes?

a. in a-thousand-years, most of our greatest monuments such as they are will have crumbled to nothing.
b. in a thousand years, most of our greatest monuments – such as they are – will have crumbled to nothing.
c. in a thousand years, most of our greatest – monuments such as – they are will have crumbled to nothing.
d. in a thousand years, most of our greatest monuments such as they are will have crumbled-to-nothing.