If something is circumscribed it is limited. Say everyday I walk the same way to work, go to the same restaurants and eat the same food. My life would be pretty circumscribed.
Circumscribe can also be used more literally, as in to draw a line around.
Dave picked up a city map and circumscribed a line around his neighborhood.
To be circumspect is to be cautious. The ‘spect’ root means to see (think of spectacles.) By extension, if you are constantly looking around you are being watchful or cautious. (Important synonyms would be wary and chary.)
New to the city, Daniel was circumspect/circumscribe when people whom he didn’t know accosted him.
This one is a little trickier. The opposite of circumscribed would be unlimited. Unbounded is a synonym for unlimited. Answer (B). Inimitable means not capable of being imitated (it’s not the answer.) And don’t get tripped up by (C). The opposite of complete is incomplete. Incomplete is not a synonym for circumscribed.