PCA (Prometheus Certified Associate) sample exam question with answer 470

Question:
Which of the following queries contains a vector matching?

1. count_values("version", build_version)
2. method_code:http_errors:rate5m{code="500"} / ignoring(code) method:http_requests:rate5m
3. sum by (app, proc) (instance_memory_limit_bytes – instance_memory_usage_bytes) / 1024 / 1024
4. sum without (instance) (http_requests_total)

Answer:
B - is correct answer. More at vector-matching
A, C, D - are incorrect. These queries does not contain a vector matching keyword (on or ignoring)