PCA (Prometheus Certified Associate) sample exam question with answer 467

Question:
Given the following two time series, what is the result of the query given below? Series:

up{job="node", instance="node1"} 0 1 1 0 1
up{job="node", instance="node2"} 1 0 1 1 1

Query:

sum(up)

1. {job="node", instance="node1"} 3
   {job="node", instance="node2"} 4

2. up{job="node", instance="node1"} 1
   up{job="node", instance="node2"} 1

3. {job="node"} 2

4. {} 2

Answer:
D - is correct. More at aggregation-operators
A - is incorrect as the sum dimensional aggregation is not aggregating by any specific labels. Thus, it will aggregate by all labels, resulting in a singular result. This would be the correct answer if the query used a temporal aggregation instead of a dimensional one: sum_over_time(up[5m])
B - is incorrect as the sum dimensional aggregation is not aggregating by any specific labels. Thus, it will aggregate by all labels, resulting in a singular result. This would be the correct answer if the query was simply up
C - is incorrect as the sum dimensional aggregation is not aggregating by any specific labels. Thus, it will aggregate across all dimensions which results in no labels being included in the query result. This would be the correct answer if the query was sum(up) by (job)