Abill can be either meaning that its contents and the discussion surrounding it are open to anyone, or meaning that most discussions about the bill take place behind closed doors and are not widely known.
a. censored . . open
b. hidden . . private
c. public . . private
d. public . . exposed

Let's first tackle the first blank space: if a bill is open to discussion for everyone, it's not censored or hidden, but it's public! So now we only need to consider options c) and d)..

The second blank talks of a bill that is discussed behind closed doors - so it's not "exposed" , but rather private - the correct answer is c)