(a) Is it an output from the system?
(d) Is it a synonym of an existing thing?
In the question,
We have a list of nouns and we need to determine whether a particular noun should be excluded by identifying particular noun as an important 'thing'.
So, to identify it as a noun we can ask two questions which will distinguish between the same.
(a) Is it an output from the system?
It is one of the questions that can be asked because if the thing is an output from a system it will be definitely existing in real therefore, we can identify from this.
(d) Is it a synonym of an existing thing?
By asking this we can also confirm whether a particular thing is a noun or not because if the thing will be a synonym for an already existing material, it definitely will be a Noun.
Therefore, the correct option is (a) and (d).