PCA (Prometheus Certified Associate) sample exam question with answer 58

Question:
Given the following two time series and assuming a scrape interval of 1m, what is the result of the query given below?
Series:

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

Query:

sum_over_time(up[5m])

1. {} 6

2. {job="node", instance="node1"} 2
   {job="node", instance="node2"} 4

3. {job="node"} 6

4. up{job="node", instance="node1"} 2
   up{job="node", instance="node2"} 4

Answer:
B - is the answer. Check aggregation over time
A - is incorrect as temporal aggregations retain the same number of results as input series
C - same as A
D - is incorrect as temporal aggregations do not retain the metric name in the result