The keyword here is 'after'. The answer must fit with 'after' and the sentence should make sense. In other words, the answer must be able to denote a time.
Option A is incorrect. 'After terrace' makes no sense as terrace denotes a place. Terrace does not fit in with 'after' and it cannot make sense of the sentence.
Option B is correct. 'After school' means 'when the school is done' which denotes a time. Thus, it not only fits with 'after' but also makes sense in the sentence.
Option C is also correct. 'After work' means 'when one is finished working' which also denotes a time. Thus, it fits with 'after' and is correct.
Option D is incorrect. Room denotes a place. It does not fit with 'after' and thus, it is incorrect.