PCA (Prometheus Certified Associate) sample exam question with answer 204

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

http_requests_total{status_code="200"} 0 1 1 2 4
http_requests_total{status_code="500"} 3 3 3 5 5

Query: changes(http_requests_total[5m])

1. http_requests_total{status_code="200"} 3
   http_requests_total{status_code="500"} 1

2. {status_code="200"} 3
   {status_code="500"} 1

3. http_requests_total{status_code="200"} 4
   http_requests_total{status_code="500"} 2

4. {status_code="200"} 4
   {status_code="500"} 2

Answer:
B - changes function gives a count of the number of times each input series has changed its value in the given range interval. Also, changes function drops the metric name from the result. Reference: changes