PCA (Prometheus Certified Associate) sample exam question with answer 244

Question:
Given the following 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 1 1 0
up{job="node", instance="node2"} 1 1 1 1 1

Query: count_over_time(up[5m])

1. {job="node", instance="node1"} 5
   {job="node", instance="node2"} 5

2. up{job="node", instance="node1"} 5
   up{job="node", instance="node2"} 5

3. {} 5

4. {job="node"} 5

Answer:
A - correct
B - is incorrect as temporal aggregations like count_over_time drop the metric name from the results
C, D - is incorrect as temporal aggregations like count_over_time act on each individual series and produce the same number of results as inputs. Thus, there should be two results, not one