PCA (Prometheus Certified Associate) sample exam question with answer 238

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(up) by (job)

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

2. {job="node"} 2

3. {} 2

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

Answer:
B - is the correct answer
A, D - is incorrect as the query counts by job so the result will only contain one result per job label
C - is incorrect as the query counts by the job label, so that label will be retained in the output